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Criteria for liver transplantation for HCC: What should the limits be?

Open AccessPublished:June 28, 2011DOI:https://doi.org/10.1016/j.jhep.2011.05.012

      Summary

      Liver transplantation is a well-established treatment in a subset of patients with cirrhosis and hepatocellular carcinoma. The Milan criteria (single nodule up to 5 cm, up to three nodules none larger than 3 cm, with no evidence of extrahepatic spread or macrovascular invasion) have been traditionally accepted as standard of care. However, some groups have proposed that these criteria are too restrictive, and exclude some patients from transplantation who might benefit from this procedure. Transplanting patients with tumors beyond the established criteria falls into two categories, those whose tumors are beyond the Milan criteria at presentation without the use of treatment prior to transplantation (expanded criteria), and those in whom treatment allows the Milan Criteria to be fulfilled (down-staging). Currently, however, there is no international consensus regarding these approaches in clinical practice. The purpose of this systematic review is to clarify this debate through a critical analysis of available data. Finally, some comments on predictive factors apart from morphological characteristics are also addressed.

      Abbreviations:

      HCC (hepatocellular carcinoma), LT (liver transplantation), UNOS (United Network for Organ Sharing), MC (Milan criteria), EASL (European Association for the Study of the Liver), AASLD (American Association for the Study of Liver Diseases), EC (expanded criteria), UCSF (University of California, San Francisco), WL (waiting list), ITT (intention-to-treat), DS (down-staging), AFP (alpha-fetoprotein), TACE (trans-arterial chemoembolization), RECIST (Response Evaluation Criteria in Solid Tumors), DCP (des-gamma-carboxy-prothrombin)

      Keywords

      Background

      Hepatocellular carcinoma (HCC) is a major health problem worldwide, accounting for more than 1 million deaths annually [
      • El-Serag H.B.
      • Rudolph K.L.
      Hepatocellular carcinoma: epidemiology and molecular carcinogenesis.
      ]. The incidence and mortality rates vary across different geographical areas because of the variation in incidence of the principal risk factors. From 60% to 90% of HCC-patients are diagnosed in association with liver cirrhosis, and the main risk factors are chronic hepatitis B and C, alcohol abuse, and non-alcoholic fatty liver disease [
      • KEW M.C.
      Hepatic tumors and cysts.
      ]. Historically, HCC was usually diagnosed late in the course of the disease and, consequently, the vast majority of patients had a poor prognosis at diagnosis, with short survival and high recurrence rates after treatment. Currently, however, as a result of the implementation of screening programs and advances in radiological assessment, an increasing proportion of patients are diagnosed with early stage disease [
      • Sherman M.
      Epidemiology of hepatocellular carcinoma.
      ]. To date, it is estimated that up to 30% of cases can be considered for treatment with a curative intent [
      • Llovet J.M.
      • Di Bisceglie A.M.
      • Bruix J.
      • Kramer B.S.
      • Lencioni R.
      • Zhu A.X.
      • et al.
      Panel of experts in HCC – design clinical trials. Design and endpoints of clinical trials in hepatocellular carcinoma.
      ]. Curative therapy includes liver resection, percutaneous ablation, and liver transplantation (LT) [
      • Bruix J.
      • Sherman M.
      • Llovet J.M.
      • Beaugrand M.
      • Lencioni R.
      • Burroughs A.K.
      • et al.
      Clinical management of hepatocellular carcinoma. Conclusions of the Barcelona 2000 EASL conference.
      ,
      • Bruix J.
      • Sherman M.
      Management of hepatocellular carcinoma.
      ].
      LT has gradually found its role in the care of patients with HCC and cirrhosis. Initially, the results of LT for HCC-patients were disappointing with high recurrence rates and dismal patient survival because of the advanced state of disease at the time of transplant [
      • Ringe B.
      • Pichlmayr R.
      • Wittekind C.
      • Tusch G.
      Surgical treatment of hepatocellular carcinoma: experience with liver resection and transplantation in 198 patients.
      ]. Therefore, the United Network for Organ Sharing (UNOS) considered HCC as a contraindication to LT, but indicated that it would be necessary to define characteristics that might be associated with better outcomes. In 1991, it was demonstrated that patients who underwent LT for reasons other than HCC, and in whom subsequent analysis of the explants identified incidental HCC, had an outcome comparable to patients who underwent LT for other indications [
      • Iwatsuki S.
      • Starzl T.E.
      • Sheahan D.G.
      • Yokohama I.
      • Demetris A.J.
      • Todo S.
      • et al.
      Hepatic resection versus transplantation for hepatocellular carcinoma.
      ]. In 1993, Bismuth et al. showed that HCC-patients who on explant examination had no more than two tumors none larger than 3 cm had good outcomes when submitted to LT [
      • Bismuth H.
      • Chiche L.
      • Adan R.
      • Castaing D.
      • Diamond T.
      • Dennison A.
      Liver resection versus transplantation in cirrhotic patients with hepatocellular carcinoma in cirrhosis.
      ]. Finally, in 1996 Mazzaferro et al. demonstrated that patients with cirrhosis and a single HCC up to 5 cm, or up to three tumors none larger than 3 cm, and without evidence of macrovascular invasion or extrahepatic spread had a 4-year post transplant survival similar to patients with non-malignant disease [
      • Mazzaferro V.
      • Regalia E.
      • Doci R.
      • Andreola S.
      • Pulvirenti A.
      • Bozzetti F.
      • et al.
      Liver transplantation for the treatment of small hepatocellular carcinomas in patients with cirrhosis.
      ]. In this study, the tumor volume was assessed on the basis of pre-transplant radiology. These criteria defined a subgroup of HCC-patients with relatively early disease, and became known as the Milan Criteria (MC). Currently, the Guidelines of the European Association for the Study of the Liver (EASL), and the American Association for the Study of Liver Diseases (AASLD) recommend that LT for HCC should be performed for patients meeting these criteria [
      • Bruix J.
      • Sherman M.
      • Llovet J.M.
      • Beaugrand M.
      • Lencioni R.
      • Burroughs A.K.
      • et al.
      Clinical management of hepatocellular carcinoma. Conclusions of the Barcelona 2000 EASL conference.
      ,
      • Bruix J.
      • Sherman M.
      Management of hepatocellular carcinoma.
      ].
      In recent years, however, some groups have argued that the MC are too restrictive, and exclude some HCC-patients from LT despite the possibility of benefit. Studies looking at liberalization of the selection criteria for LT for HCC take two forms. One form relates to transplantation of patients whose tumors are beyond the MC without using pre-LT treatment (expanded criteria). The second form involves the use of treatment to convert lesions that exceed MC to lesions that are anatomically within the MC (down-staging). Currently, however, there is no international consensus about adopting these alternatives as standard of care [
      • Yao F.Y.
      Expanded criteria for hepatocellular carcinoma: down-staging with a view to liver transplantation – Yes.
      ,
      • Llovet J.M.
      • Schwartz M.
      • Fuster J.
      • Bruix J.
      Expanded criteria for hepatocellular carcinoma through down-staging prior to liver transplantation: not yet there.
      ]. The purpose of this systematic review is to clarify this debate through a critical analysis of available data. Moreover, the discussion of further parameters beyond number and size of tumor is also addressed.

      Data search methodology

      A systematic search of Medline database was performed to identify studies evaluating expanded criteria and down-staging therapy of hepatocellular carcinoma. The search was restricted to papers written in English and published from 1995 to 2010. The keywords used were hepatocellular carcinoma, HCC, liver transplantation, LT, OLT, down-staging, expanded criteria, the UCSF criteria, and Milan criteria. Only papers reporting cadaveric liver donors that evaluated expanded criteria and down-staging on the basis of tumor number and size were selected. This search resulted in a total of 49 studies. Additionally, a full manual search from bibliographies of papers describing aspects beyond tumor number and size, and reports of consensus conference was also performed.
      Figure thumbnail fx4

      Selection criteria for liver transplantation in HCC-patients

      Transplanting HCC-patients with tumors beyond the Milan criteria

      Expanded criteria (EC) can be defined by the use of LT in recipients with tumors beyond the MC. The first description was published in 2001 by the group of the University of California, San Francisco (UCSF) [
      • Yao F.Y.
      • Ferrell L.
      • Bass N.M.
      • Watson J.J.
      • Bacchetti P.
      • Venook A.
      • et al.
      Liver transplantation for hepatocellular carcinoma: expansion of the tumor size limits does not adversely impact survival.
      ]. In their study, 70 HCC-patients who underwent LT were retrospectively evaluated on the basis of explant analysis, not pre-transplant radiology. In the 60 cases with either a single nodule up to 6.5 cm, or up to three nodules none larger than 4.5 cm, and total tumor diameter no more than 8 cm the 5-year overall survival was 75.2%. Forty-six out of the 60 patients (76%) had tumors that were within the MC and these had a 5-year survival of 72%. Subsequently, a number of different EC proposals have been described (Table 1) [
      • Herrero J.I.
      • Sangro B.
      • Quiroga J.
      • Pardo F.
      • Herraiz M.
      • Cienfuegos J.A.
      • et al.
      Influence of tumor characteristics on the outcome of liver transplantation among patients with liver cirrhosis and hepatocellular carcinoma.
      ,
      • Roayaie S.
      • Frischer J.
      • Emre S.H.
      • Fishbein T.M.
      • Sheiner P.A.
      • Sung M.
      • et al.
      Long-term results with multimodal adjuvant therapy and liver transplantation for the treatment of hepatocellular carcinomas larger than 5 centimeters.
      ,
      • Khakhar A.
      • Solano E.
      • Stell D.
      • Bloch M.
      • Dale C.
      • Burns P.
      • et al.
      Survival after liver transplantation for hepatocellular carcinoma.
      ,
      • Fernández J.A.
      • Rob R.
      • Marin C.
      • Sánchez Bueno F.
      • Ramirez P.
      • Pons J.A.
      • et al.
      Can we expand the indications for liver transplantation among hepatocellular carcinoma patients with increased tumor size?.
      ,
      • Marsh J.W.
      • Dvorchik I.
      Liver organ allocation for hepatocellular carcinoma: are we sure?.
      ,
      • Ravaioli M.
      • Ercolani G.
      • Cescon M.
      • Vetrone G.
      • Voci C.
      • Grigioni W.F.
      • et al.
      Liver transplantation for hepatocellular carcinoma: further considerations on selection criteria.
      ,
      • Kneteman N.M.
      • Oberholzer J.
      • Saghier M.A.
      • Meeberg G.A.
      • Blitz M.
      • Ma M.M.
      • et al.
      Sirolimus-based immunosuppression for liver transplantation in the presence of extended criteria for hepatocellular carcinoma.
      ,
      • Leung J.Y.
      • Zhu A.X.
      • Gordon F.D.
      • Pratt D.S.
      • Mithoefer A.
      • Garrigan K.
      • et al.
      Liver transplantation outcome for early-stage hepatocellular carcinoma: results of a multicenter study.
      ,
      • Zavaglia C.
      • De Carlis L.
      • Alberti A.B.
      • Minola E.
      • Belli L.S.
      • Alim A.O.
      • et al.
      Predictors of long-term survival after liver transplantation for hepatocellular carcinoma.
      ,
      • Löhe F.
      • Angele M.K.
      • Gerbes A.L.
      • Löhrs U.
      • Jauch K.W.
      • Schauer R.J.
      Tumour size is an important predictor for the outcome after liver transplantation for hepatocellular carcinoma.
      ,
      • Decaens T.
      • Roudot-Thoraval F.
      • Hadni-Bresson S.
      • Meyer C.
      • Gugenheim J.
      • Durand F.
      • et al.
      Impact of UCLA criteria according to pre-and post-OLT tumor features: analysis of 479 patients listed for HCC with a short waiting time.
      ,
      • Onaca N.
      • Gary L.D.
      • Goldstein R.M.
      • Jennings L.W.
      • Klintmalm G.B.
      Expanded criteria for liver transplantation in patients with hepatocellular carcinoma: a report from the International Registry of Hepatic Tumors in Liver Transplantation.
      ,
      • Parfitt J.R.
      • Marotta P.
      • Alghamdi M.
      • Wall W.
      • Khakhar A.
      • Suskin N.G.
      • et al.
      Recurrent hepatocellular carcinoma after transplantation: use of a pathological score on explanted livers to predict recurrence.
      ,
      • Duffy J.P.
      • Vardanian A.
      • Benjamin E.
      • Watson M.
      • Farmer D.G.
      • Ghobrial R.M.
      • et al.
      Liver transplantation criteria for hepatocellular carcinoma should be expanded: a 22-year experience with 467 patients at UCLA.
      ,
      • Yao F.Y.
      • Xiao L.
      • Bass N.M.
      • Kerlan R.
      • Ascher N.R.
      • Roberts J.P.
      Liver transplantation for hepatocellular carcinoma: validation of the UCSF-expanded criteria based on preoperative imaging.
      ,
      • Jun C.
      • Xiao X.
      • Qi L.
      • Jian W.U.
      • Shu-sen Z.
      Role of Pittsburgh modified TNM criteria in prognosis prediction of liver transplantation for hepatocellular carcinoma.
      ,
      • Suh K.S.
      • Cho E.H.
      • Lee H.W.
      • Chin W.Y.
      • Yi N.J.
      • Lee K.U.
      Liver transplantation for hepatocellular carcinoma in patients who do not meet the Milan criteria.
      ,
      • Herrero J.A.
      • Sangro B.
      • Pardo F.
      • Quiroga J.
      • Iñarrairaegui M.
      • Rottelar F.
      • et al.
      Liver transplantation in patients with hepatocellular carcinoma across Milan criteria.
      ,
      • Toso C.
      • Troter J.
      • Wei A.
      • Bigam D.L.
      • Shah S.
      • Lancaster J.
      • et al.
      Total tumor volume predicts risk of recurrence following liver transplantation in patients with hepatocellular carcinoma.
      ,
      • Silva M.
      • Moya A.
      • Berenguer M.
      • Sanjuan F.
      • López-Andujar R.
      • Pareja E.
      • et al.
      Expanded criteria for liver transplantation in patients with cirrhosis and hepatocellular carcinoma.
      ,
      • Mazzaferro V.
      • Llovet J.M.
      • Miceli R.
      • Bhoori S.
      • Schiavo M.
      • Mariani L.
      • et al.
      Predicting survival after liver transplantation in patients with hepatocellular carcinoma beyond the Milan criteria: a retrospective, exploratory analysis.
      ,
      • Pelletier S.J.
      • Fu S.
      • Thyagarajan V.
      • Romero-Marrero C.
      • Batheja M.
      • Punch J.D.
      • et al.
      An intention-to-treat analysis of liver transplantation for hepatocellular carcinoma using organ procurement transplant data.
      ,
      • Fan J.
      • Yang G.S.
      • Fu Z.R.
      • Peng Z.H.
      • Xia Q.
      • Peng C.H.
      • et al.
      Liver transplantation outcome in 1,078 hepatocellular carcinoma patients: a multi-center experience in Shanghai, China.
      ,
      • Chen J.W.C.
      • Kow L.
      • Verran D.J.
      • McCall J.L.
      • Munn S.
      • Balderson J.A.
      • et al.
      Poorer survival in patients whose explanted hepatocellular carcinoma (HCC) excedes Milano or UCSF criteria. An analysis of liver transplantation in HCC in Australia and New Zealand.
      ,
      • Toso C.
      • Asthana S.
      • Bigam D.L.
      • Shapiro M.J.
      • Kneteman N.M.
      Reassessing selection criteria prior to liver transplantation for hepatocellular carcinoma utilizing the scientific registry of transplant recipients database.
      ,
      • Gabrielli M.
      • Vivanco M.
      • Hepp J.
      • Martínez J.
      • Pérez R.
      • Guerra J.
      • et al.
      Liver transplantation results for hepatocellular carcinoma in Chile.
      ,
      • Guiteau J.J.
      • Cotton R.T.
      • Washburn W.K.
      • Harper A.
      • O’Mahony C.A.
      • Sebastian A.
      • et al.
      An early regional experience with expansion of Milan criteria for liver transplant recipients.
      ]. However, the robustness of the data among these studies deserves special attention in several aspects.
      Table 1Results from studies evaluating down-staging for cadaveric liver transplantation for patients with cirrhosis and hepatocellular carcinoma.
      aIntention-to-treat principle.
      bRecurrence-free survival.
      MC, Milan criteria; UCSF, University of California, San Francisco; N/A, not available; HCC, hepatocellular carcinoma; TACE, transarterial chemoembolization, LT, liver transplantation; UNOS, United Network for Organ Sharing; AFP, alpha-fetoprotein.

      Method of tumor assessment

      Despite the recent advancements in radiological assessment of liver masses [
      • Sherman M.
      The radiological diagnosis of hepatocellular carcinoma.
      ], the risk of underestimating tumor burden is still a major concern. Freeman et al. evaluated the results from UNOS database on 789 LT recipients to determine the accuracy of pre-LT imaging compared with explant features [
      • Freeman R.B.
      • Mithoefer A.
      • Ruthazer R.
      • Nguyen K.
      • Schore A.
      • Harper A.
      • et al.
      Optimizing staging of hepatocellular carcinoma before liver transplantation: a retrospective analysis of the UNOS/OPTN database.
      ]. No patients had received any treatment prior to LT, and at least 83% of cases were preoperatively staged through computed tomography or magnetic resonance. Using the American Liver Tumor Study Group TNM staging [

      American Liver Tumor Study Group. A randomized prospective multi-institutional trial for orthotopic liver transplantation or partial hepatic resection with or without adjuvant chemotherapy for hepatocellular carcinoma. Investigators booklet and protocol; 1998.

      ], radiology underestimated tumor staging in 26.6% of cases. Furthermore, the risk of overestimation was almost 30%. The overall preoperative accuracy was around 50%, regardless of the radiological technique used. Whether this is due to inherent shortcomings of cross sectional imaging techniques or to less than optimal protocols or interpretive expertise is not clear. While this may not be important when using MC, because the criteria allow some leeway, radiological understating may be much more important when working at the limits of what may be an acceptable size of lesion for transplant, such as with the UCSF criteria. Of the studies shown in Table 1, only four evaluated the risk of underestimating tumor size separately in patients within the MC and beyond the MC but within the proposed selection criteria [
      • Decaens T.
      • Roudot-Thoraval F.
      • Hadni-Bresson S.
      • Meyer C.
      • Gugenheim J.
      • Durand F.
      • et al.
      Impact of UCLA criteria according to pre-and post-OLT tumor features: analysis of 479 patients listed for HCC with a short waiting time.
      ,
      • Yao F.Y.
      • Xiao L.
      • Bass N.M.
      • Kerlan R.
      • Ascher N.R.
      • Roberts J.P.
      Liver transplantation for hepatocellular carcinoma: validation of the UCSF-expanded criteria based on preoperative imaging.
      ,
      • Toso C.
      • Troter J.
      • Wei A.
      • Bigam D.L.
      • Shah S.
      • Lancaster J.
      • et al.
      Total tumor volume predicts risk of recurrence following liver transplantation in patients with hepatocellular carcinoma.
      ,
      • Silva M.
      • Moya A.
      • Berenguer M.
      • Sanjuan F.
      • López-Andujar R.
      • Pareja E.
      • et al.
      Expanded criteria for liver transplantation in patients with cirrhosis and hepatocellular carcinoma.
      ]. The Valencia proposal (up to three nodules, none larger than 5 cm, and a cumulative tumor burden of 10 cm, without macrovascular invasion or extrahepatic spread) showed that the preoperative radiological assessment underestimated tumor size in 38.5% of the cases beyond the MC, but only 17.3% in patients within the MC (p= 0.014) [
      • Silva M.
      • Moya A.
      • Berenguer M.
      • Sanjuan F.
      • López-Andujar R.
      • Pareja E.
      • et al.
      Expanded criteria for liver transplantation in patients with cirrhosis and hepatocellular carcinoma.
      ]. Decaens et al. did a similar analysis using the UCSF criteria [
      • Decaens T.
      • Roudot-Thoraval F.
      • Hadni-Bresson S.
      • Meyer C.
      • Gugenheim J.
      • Durand F.
      • et al.
      Impact of UCLA criteria according to pre-and post-OLT tumor features: analysis of 479 patients listed for HCC with a short waiting time.
      ]. Radiology underestimated tumor size in 48% of the cases beyond the MC and 34% in patients within the UCSF criteria (p= 0.09). On the other hand, Yao et al. did not find higher rates of radiological underestimation when they compared the MC with the UCSF proposal (p= 0.26). In this study the number of cases in the EC group was small, only 38 cases [
      • Yao F.Y.
      • Xiao L.
      • Bass N.M.
      • Kerlan R.
      • Ascher N.R.
      • Roberts J.P.
      Liver transplantation for hepatocellular carcinoma: validation of the UCSF-expanded criteria based on preoperative imaging.
      ]. Finally, Toso et al. showed that their proposal based on total tumor volume with a cutoff of 115 cm3 was more likely to result in correct staging prior to LT when comparing patients with tumors within the MC or within the UCSF criteria (91% vs. 69% and 75%, respectively, p<0.001). Most importantly, various studies have shown higher recurrence probability and worse survival in cases who had tumors staged inaccurately [
      • Herrero J.I.
      • Sangro B.
      • Quiroga J.
      • Pardo F.
      • Herraiz M.
      • Cienfuegos J.A.
      • et al.
      Influence of tumor characteristics on the outcome of liver transplantation among patients with liver cirrhosis and hepatocellular carcinoma.
      ,
      • Ravaioli M.
      • Ercolani G.
      • Cescon M.
      • Vetrone G.
      • Voci C.
      • Grigioni W.F.
      • et al.
      Liver transplantation for hepatocellular carcinoma: further considerations on selection criteria.
      ,
      • Leung J.Y.
      • Zhu A.X.
      • Gordon F.D.
      • Pratt D.S.
      • Mithoefer A.
      • Garrigan K.
      • et al.
      Liver transplantation outcome for early-stage hepatocellular carcinoma: results of a multicenter study.
      ,
      • Decaens T.
      • Roudot-Thoraval F.
      • Hadni-Bresson S.
      • Meyer C.
      • Gugenheim J.
      • Durand F.
      • et al.
      Impact of UCLA criteria according to pre-and post-OLT tumor features: analysis of 479 patients listed for HCC with a short waiting time.
      ,
      • Duffy J.P.
      • Vardanian A.
      • Benjamin E.
      • Watson M.
      • Farmer D.G.
      • Ghobrial R.M.
      • et al.
      Liver transplantation criteria for hepatocellular carcinoma should be expanded: a 22-year experience with 467 patients at UCLA.
      ,
      • Yao F.Y.
      • Xiao L.
      • Bass N.M.
      • Kerlan R.
      • Ascher N.R.
      • Roberts J.P.
      Liver transplantation for hepatocellular carcinoma: validation of the UCSF-expanded criteria based on preoperative imaging.
      ,
      • Toso C.
      • Troter J.
      • Wei A.
      • Bigam D.L.
      • Shah S.
      • Lancaster J.
      • et al.
      Total tumor volume predicts risk of recurrence following liver transplantation in patients with hepatocellular carcinoma.
      ,
      • Silva M.
      • Moya A.
      • Berenguer M.
      • Sanjuan F.
      • López-Andujar R.
      • Pareja E.
      • et al.
      Expanded criteria for liver transplantation in patients with cirrhosis and hepatocellular carcinoma.
      ,
      • Pelletier S.J.
      • Fu S.
      • Thyagarajan V.
      • Romero-Marrero C.
      • Batheja M.
      • Punch J.D.
      • et al.
      An intention-to-treat analysis of liver transplantation for hepatocellular carcinoma using organ procurement transplant data.
      ,
      • Chen J.W.C.
      • Kow L.
      • Verran D.J.
      • McCall J.L.
      • Munn S.
      • Balderson J.A.
      • et al.
      Poorer survival in patients whose explanted hepatocellular carcinoma (HCC) excedes Milano or UCSF criteria. An analysis of liver transplantation in HCC in Australia and New Zealand.
      ].

      The dilution effect

      Whatever expanded proposal is analyzed, the impact of the dilution effect on outcomes is important and not fully accounted for. For instance, the pioneer paper published by the UCSF group described their results adopting an expanded proposal without analyzing patients within and beyond the MC separately [
      • Yao F.Y.
      • Ferrell L.
      • Bass N.M.
      • Watson J.J.
      • Bacchetti P.
      • Venook A.
      • et al.
      Liver transplantation for hepatocellular carcinoma: expansion of the tumor size limits does not adversely impact survival.
      ]. The dilution effect has a paramount role since both tumor recurrence and patient survival may be persuasive because of the inclusion of cases having in theory the best characteristics such as the group within the MC. In the original UCSF study, only 24% of cases were beyond MC. As Table 1 shows, more recent studies that have evaluated the possibility of expanding the MC have taken this into account [
      • Khakhar A.
      • Solano E.
      • Stell D.
      • Bloch M.
      • Dale C.
      • Burns P.
      • et al.
      Survival after liver transplantation for hepatocellular carcinoma.
      ,
      • Fernández J.A.
      • Rob R.
      • Marin C.
      • Sánchez Bueno F.
      • Ramirez P.
      • Pons J.A.
      • et al.
      Can we expand the indications for liver transplantation among hepatocellular carcinoma patients with increased tumor size?.
      ,
      • Ravaioli M.
      • Ercolani G.
      • Cescon M.
      • Vetrone G.
      • Voci C.
      • Grigioni W.F.
      • et al.
      Liver transplantation for hepatocellular carcinoma: further considerations on selection criteria.
      ,
      • Kneteman N.M.
      • Oberholzer J.
      • Saghier M.A.
      • Meeberg G.A.
      • Blitz M.
      • Ma M.M.
      • et al.
      Sirolimus-based immunosuppression for liver transplantation in the presence of extended criteria for hepatocellular carcinoma.
      ,
      • Decaens T.
      • Roudot-Thoraval F.
      • Hadni-Bresson S.
      • Meyer C.
      • Gugenheim J.
      • Durand F.
      • et al.
      Impact of UCLA criteria according to pre-and post-OLT tumor features: analysis of 479 patients listed for HCC with a short waiting time.
      ,
      • Onaca N.
      • Gary L.D.
      • Goldstein R.M.
      • Jennings L.W.
      • Klintmalm G.B.
      Expanded criteria for liver transplantation in patients with hepatocellular carcinoma: a report from the International Registry of Hepatic Tumors in Liver Transplantation.
      ,
      • Parfitt J.R.
      • Marotta P.
      • Alghamdi M.
      • Wall W.
      • Khakhar A.
      • Suskin N.G.
      • et al.
      Recurrent hepatocellular carcinoma after transplantation: use of a pathological score on explanted livers to predict recurrence.
      ,
      • Duffy J.P.
      • Vardanian A.
      • Benjamin E.
      • Watson M.
      • Farmer D.G.
      • Ghobrial R.M.
      • et al.
      Liver transplantation criteria for hepatocellular carcinoma should be expanded: a 22-year experience with 467 patients at UCLA.
      ,
      • Yao F.Y.
      • Xiao L.
      • Bass N.M.
      • Kerlan R.
      • Ascher N.R.
      • Roberts J.P.
      Liver transplantation for hepatocellular carcinoma: validation of the UCSF-expanded criteria based on preoperative imaging.
      ,
      • Suh K.S.
      • Cho E.H.
      • Lee H.W.
      • Chin W.Y.
      • Yi N.J.
      • Lee K.U.
      Liver transplantation for hepatocellular carcinoma in patients who do not meet the Milan criteria.
      ,
      • Herrero J.A.
      • Sangro B.
      • Pardo F.
      • Quiroga J.
      • Iñarrairaegui M.
      • Rottelar F.
      • et al.
      Liver transplantation in patients with hepatocellular carcinoma across Milan criteria.
      ,
      • Toso C.
      • Troter J.
      • Wei A.
      • Bigam D.L.
      • Shah S.
      • Lancaster J.
      • et al.
      Total tumor volume predicts risk of recurrence following liver transplantation in patients with hepatocellular carcinoma.
      ,
      • Silva M.
      • Moya A.
      • Berenguer M.
      • Sanjuan F.
      • López-Andujar R.
      • Pareja E.
      • et al.
      Expanded criteria for liver transplantation in patients with cirrhosis and hepatocellular carcinoma.
      ,
      • Mazzaferro V.
      • Llovet J.M.
      • Miceli R.
      • Bhoori S.
      • Schiavo M.
      • Mariani L.
      • et al.
      Predicting survival after liver transplantation in patients with hepatocellular carcinoma beyond the Milan criteria: a retrospective, exploratory analysis.
      ,
      • Pelletier S.J.
      • Fu S.
      • Thyagarajan V.
      • Romero-Marrero C.
      • Batheja M.
      • Punch J.D.
      • et al.
      An intention-to-treat analysis of liver transplantation for hepatocellular carcinoma using organ procurement transplant data.
      ,
      • Fan J.
      • Yang G.S.
      • Fu Z.R.
      • Peng Z.H.
      • Xia Q.
      • Peng C.H.
      • et al.
      Liver transplantation outcome in 1,078 hepatocellular carcinoma patients: a multi-center experience in Shanghai, China.
      ,
      • Gabrielli M.
      • Vivanco M.
      • Hepp J.
      • Martínez J.
      • Pérez R.
      • Guerra J.
      • et al.
      Liver transplantation results for hepatocellular carcinoma in Chile.
      ,
      • Guiteau J.J.
      • Cotton R.T.
      • Washburn W.K.
      • Harper A.
      • O’Mahony C.A.
      • Sebastian A.
      • et al.
      An early regional experience with expansion of Milan criteria for liver transplant recipients.
      ].

      Upper tumor size limits

      There is a general agreement among different proposals that patients presenting macrovascular invasion or extrahepatic spread should be excluded from LT given the unacceptable recurrence risk. Only the studies published by Roayaie et al. and Suh et al. suggested that tumor involvement of portal branches was not a contraindication to LT [
      • Roayaie S.
      • Frischer J.
      • Emre S.H.
      • Fishbein T.M.
      • Sheiner P.A.
      • Sung M.
      • et al.
      Long-term results with multimodal adjuvant therapy and liver transplantation for the treatment of hepatocellular carcinomas larger than 5 centimeters.
      ,
      • Suh K.S.
      • Cho E.H.
      • Lee H.W.
      • Chin W.Y.
      • Yi N.J.
      • Lee K.U.
      Liver transplantation for hepatocellular carcinoma in patients who do not meet the Milan criteria.
      ]. Given that the MC exclude these characteristics, it is important that any new proposal for EC describes in detail the specific proposal. A description of cases as simply “beyond the MC” has only limited value because of the lack of information about the exact features in this group. This subset of patients could include cases with any single nodules larger than 5 cm, any cases with two or three nodules larger than 3 cm, or any cases with more than three nodules. Unfortunately, some of the papers described in Table 1 do not describe the tumor upper limits. Studies from UCSF, Navarra, Alberta, Valencia, Shanghai, the Metroticket study, and the UNOS Region 4 groups [
      • Yao F.Y.
      • Ferrell L.
      • Bass N.M.
      • Watson J.J.
      • Bacchetti P.
      • Venook A.
      • et al.
      Liver transplantation for hepatocellular carcinoma: expansion of the tumor size limits does not adversely impact survival.
      ,
      • Herrero J.I.
      • Sangro B.
      • Quiroga J.
      • Pardo F.
      • Herraiz M.
      • Cienfuegos J.A.
      • et al.
      Influence of tumor characteristics on the outcome of liver transplantation among patients with liver cirrhosis and hepatocellular carcinoma.
      ,
      • Toso C.
      • Troter J.
      • Wei A.
      • Bigam D.L.
      • Shah S.
      • Lancaster J.
      • et al.
      Total tumor volume predicts risk of recurrence following liver transplantation in patients with hepatocellular carcinoma.
      ,
      • Silva M.
      • Moya A.
      • Berenguer M.
      • Sanjuan F.
      • López-Andujar R.
      • Pareja E.
      • et al.
      Expanded criteria for liver transplantation in patients with cirrhosis and hepatocellular carcinoma.
      ,
      • Mazzaferro V.
      • Llovet J.M.
      • Miceli R.
      • Bhoori S.
      • Schiavo M.
      • Mariani L.
      • et al.
      Predicting survival after liver transplantation in patients with hepatocellular carcinoma beyond the Milan criteria: a retrospective, exploratory analysis.
      ,
      • Fan J.
      • Yang G.S.
      • Fu Z.R.
      • Peng Z.H.
      • Xia Q.
      • Peng C.H.
      • et al.
      Liver transplantation outcome in 1,078 hepatocellular carcinoma patients: a multi-center experience in Shanghai, China.
      ] do provide upper limits of tumor size. Kneteman et al. also described an expanded proposal from the Canadian Liver Transplant Study Group [
      • Kneteman N.M.
      • Oberholzer J.
      • Saghier M.A.
      • Meeberg G.A.
      • Blitz M.
      • Ma M.M.
      • et al.
      Sirolimus-based immunosuppression for liver transplantation in the presence of extended criteria for hepatocellular carcinoma.
      ]. Adopting a sirulimus-based immunosuppression protocol, survival rates, and tumor recurrence were compared between patients within (n = 18) and beyond the MC (n = 9). Inclusion criteria were broadened to include patients with single tumors up to 7.5 cm or any number of tumors none larger than 5 cm in diameter. Patients with tumors larger than 5 cm based on radiology were routinely biopsied and excluded from LT if there was poor differentiation. Despite similar long-term survival in both groups, given that there was no restriction in tumor number, an absence of a detailed description of tumor characteristics and a very small sample size, this proposal needs to be cautiously interpreted.

      Intention-to-treat principle

      Dropout from the waiting list (WL) secondary to tumor progression has recently become an area of major relevance. Currently, there are no well-defined characteristics that predict who is more likely to be removed from the WL as a result of tumor progression beyond the listing criteria. The Barcelona group has shown that in patients with tumors within MC, the 6-month cumulative probability of dropout was 11%, growing to 38% in the end of the first year on WL [
      • Llovet J.M.
      • Fuster J.
      • Bruix J.
      Intention-to-treat analysis of surgical treatment for early hepatocellular carcinoma: resection versus transplantation.
      ]. Additionally, it was demonstrated that if the dropout rate is 25% at 12 months, the 5-year survival was 60% based on the intention-to-treat principle (IIT), compared to 70–80% described for patients within the MC who actually get transplanted. In the setting of EC, it could be argued that the probability of dropout will be even higher as time goes by, when compared with patients within the MC. Few studies have analyzed EC by the ITT principle [
      • Decaens T.
      • Roudot-Thoraval F.
      • Hadni-Bresson S.
      • Meyer C.
      • Gugenheim J.
      • Durand F.
      • et al.
      Impact of UCLA criteria according to pre-and post-OLT tumor features: analysis of 479 patients listed for HCC with a short waiting time.
      ,
      • Herrero J.A.
      • Sangro B.
      • Pardo F.
      • Quiroga J.
      • Iñarrairaegui M.
      • Rottelar F.
      • et al.
      Liver transplantation in patients with hepatocellular carcinoma across Milan criteria.
      ,
      • Silva M.
      • Moya A.
      • Berenguer M.
      • Sanjuan F.
      • López-Andujar R.
      • Pareja E.
      • et al.
      Expanded criteria for liver transplantation in patients with cirrhosis and hepatocellular carcinoma.
      ,
      • Pelletier S.J.
      • Fu S.
      • Thyagarajan V.
      • Romero-Marrero C.
      • Batheja M.
      • Punch J.D.
      • et al.
      An intention-to-treat analysis of liver transplantation for hepatocellular carcinoma using organ procurement transplant data.
      ]. Two of these papers showed a 5-year survival rate less than 50%, a level that has been considered as the lowest acceptable outcome [
      • Decaens T.
      • Roudot-Thoraval F.
      • Hadni-Bresson S.
      • Meyer C.
      • Gugenheim J.
      • Durand F.
      • et al.
      Impact of UCLA criteria according to pre-and post-OLT tumor features: analysis of 479 patients listed for HCC with a short waiting time.
      ,
      • Pelletier S.J.
      • Fu S.
      • Thyagarajan V.
      • Romero-Marrero C.
      • Batheja M.
      • Punch J.D.
      • et al.
      An intention-to-treat analysis of liver transplantation for hepatocellular carcinoma using organ procurement transplant data.
      ]. Interestingly, it is important to note that this phenomenon has already been shown in a subset of patients with tumors within the MC. Yao et al. showed that patients having single nodules larger than 3 cm, or more than one nodule presented a dropout probability that was higher than those with a single nodule up to 3 cm [
      • Yao F.Y.
      • Bass N.M.
      • Nicolai B.
      • Davern T.J.
      • Kerlan R.
      • Wu V.
      • et al.
      Liver transplantation for hepatocellular carcinoma: analysis of survival according to the intention-to-treat principle, and a dropout from the waiting list.
      ]. There are two approaches that can be considered. The first is to exclude patients with these adverse tumor characteristics from transplant or alternatively prioritize these cases for early LT. Furthermore, efforts should be made to identify factors associated with dropout in order, once again, to prioritize these patients for transplant. Of course, it could be that those factors that predict dropout also predict worse prognosis after transplant. This too requires study.

      Study design

      Most of EC proposals have been developed on the basis of retrospective studies [
      • Yao F.Y.
      • Ferrell L.
      • Bass N.M.
      • Watson J.J.
      • Bacchetti P.
      • Venook A.
      • et al.
      Liver transplantation for hepatocellular carcinoma: expansion of the tumor size limits does not adversely impact survival.
      ,
      • Khakhar A.
      • Solano E.
      • Stell D.
      • Bloch M.
      • Dale C.
      • Burns P.
      • et al.
      Survival after liver transplantation for hepatocellular carcinoma.
      ,
      • Fernández J.A.
      • Rob R.
      • Marin C.
      • Sánchez Bueno F.
      • Ramirez P.
      • Pons J.A.
      • et al.
      Can we expand the indications for liver transplantation among hepatocellular carcinoma patients with increased tumor size?.
      ,
      • Marsh J.W.
      • Dvorchik I.
      Liver organ allocation for hepatocellular carcinoma: are we sure?.
      ,
      • Ravaioli M.
      • Ercolani G.
      • Cescon M.
      • Vetrone G.
      • Voci C.
      • Grigioni W.F.
      • et al.
      Liver transplantation for hepatocellular carcinoma: further considerations on selection criteria.
      ,
      • Leung J.Y.
      • Zhu A.X.
      • Gordon F.D.
      • Pratt D.S.
      • Mithoefer A.
      • Garrigan K.
      • et al.
      Liver transplantation outcome for early-stage hepatocellular carcinoma: results of a multicenter study.
      ,
      • Zavaglia C.
      • De Carlis L.
      • Alberti A.B.
      • Minola E.
      • Belli L.S.
      • Alim A.O.
      • et al.
      Predictors of long-term survival after liver transplantation for hepatocellular carcinoma.
      ,
      • Löhe F.
      • Angele M.K.
      • Gerbes A.L.
      • Löhrs U.
      • Jauch K.W.
      • Schauer R.J.
      Tumour size is an important predictor for the outcome after liver transplantation for hepatocellular carcinoma.
      ,
      • Decaens T.
      • Roudot-Thoraval F.
      • Hadni-Bresson S.
      • Meyer C.
      • Gugenheim J.
      • Durand F.
      • et al.
      Impact of UCLA criteria according to pre-and post-OLT tumor features: analysis of 479 patients listed for HCC with a short waiting time.
      ,
      • Onaca N.
      • Gary L.D.
      • Goldstein R.M.
      • Jennings L.W.
      • Klintmalm G.B.
      Expanded criteria for liver transplantation in patients with hepatocellular carcinoma: a report from the International Registry of Hepatic Tumors in Liver Transplantation.
      ,
      • Parfitt J.R.
      • Marotta P.
      • Alghamdi M.
      • Wall W.
      • Khakhar A.
      • Suskin N.G.
      • et al.
      Recurrent hepatocellular carcinoma after transplantation: use of a pathological score on explanted livers to predict recurrence.
      ,
      • Duffy J.P.
      • Vardanian A.
      • Benjamin E.
      • Watson M.
      • Farmer D.G.
      • Ghobrial R.M.
      • et al.
      Liver transplantation criteria for hepatocellular carcinoma should be expanded: a 22-year experience with 467 patients at UCLA.
      ,
      • Jun C.
      • Xiao X.
      • Qi L.
      • Jian W.U.
      • Shu-sen Z.
      Role of Pittsburgh modified TNM criteria in prognosis prediction of liver transplantation for hepatocellular carcinoma.
      ,
      • Suh K.S.
      • Cho E.H.
      • Lee H.W.
      • Chin W.Y.
      • Yi N.J.
      • Lee K.U.
      Liver transplantation for hepatocellular carcinoma in patients who do not meet the Milan criteria.
      ,
      • Toso C.
      • Troter J.
      • Wei A.
      • Bigam D.L.
      • Shah S.
      • Lancaster J.
      • et al.
      Total tumor volume predicts risk of recurrence following liver transplantation in patients with hepatocellular carcinoma.
      ,
      • Silva M.
      • Moya A.
      • Berenguer M.
      • Sanjuan F.
      • López-Andujar R.
      • Pareja E.
      • et al.
      Expanded criteria for liver transplantation in patients with cirrhosis and hepatocellular carcinoma.
      ,
      • Mazzaferro V.
      • Llovet J.M.
      • Miceli R.
      • Bhoori S.
      • Schiavo M.
      • Mariani L.
      • et al.
      Predicting survival after liver transplantation in patients with hepatocellular carcinoma beyond the Milan criteria: a retrospective, exploratory analysis.
      ,
      • Pelletier S.J.
      • Fu S.
      • Thyagarajan V.
      • Romero-Marrero C.
      • Batheja M.
      • Punch J.D.
      • et al.
      An intention-to-treat analysis of liver transplantation for hepatocellular carcinoma using organ procurement transplant data.
      ,
      • Fan J.
      • Yang G.S.
      • Fu Z.R.
      • Peng Z.H.
      • Xia Q.
      • Peng C.H.
      • et al.
      Liver transplantation outcome in 1,078 hepatocellular carcinoma patients: a multi-center experience in Shanghai, China.
      ,
      • Chen J.W.C.
      • Kow L.
      • Verran D.J.
      • McCall J.L.
      • Munn S.
      • Balderson J.A.
      • et al.
      Poorer survival in patients whose explanted hepatocellular carcinoma (HCC) excedes Milano or UCSF criteria. An analysis of liver transplantation in HCC in Australia and New Zealand.
      ,
      • Toso C.
      • Asthana S.
      • Bigam D.L.
      • Shapiro M.J.
      • Kneteman N.M.
      Reassessing selection criteria prior to liver transplantation for hepatocellular carcinoma utilizing the scientific registry of transplant recipients database.
      ,
      • Gabrielli M.
      • Vivanco M.
      • Hepp J.
      • Martínez J.
      • Pérez R.
      • Guerra J.
      • et al.
      Liver transplantation results for hepatocellular carcinoma in Chile.
      ]. Prospective study design has been ranked higher in the hierarchy of evidence than retrospective evaluation [
      • Moher D.
      • Dulberg C.S.
      • Wells G.A.
      Statistical power, sample size, and their reporting in randomized controlled trials.
      ,
      • Vandenbroucke J.P.
      Prospective or retrospective: what’s in a name?.
      ,
      • Euser A.N.
      • Zoccali C.
      • Jager K.J.
      • Dekker F.W.
      Cohort studies: prospective versus retrospective.
      ]. The major strength of a prospective cohort study is the accuracy of data collection with regards to exposures, confounding factors, and outcomes, and restriction of study participants to those with pre-defined characteristics. Given that the main concern related to the possibility of MC expansion is the decrease in survival as a result of tumor recurrence, this event may be underestimated using retrospective cohorts, since radiological assessment is less likely to be performed strictly, and follow-up may be incomplete. Thus, any proposal to expand the MC should be ideally designed prospectively. Looking at Table 1, some studies evaluated the use of more liberal criteria through a prospective design. These will be commented on separately later.

      Statistical power

      The comparison between patients within and beyond MC may show similar survival rates as a result of the analysis of an insufficient number of patients to show true outcome differences. There is no universal rule in order to calculate the number of patients that should be followed. Dr. Andrew Burroughs has recently performed a systematic review of patients who underwent LT with tumors within the MC on the basis of radiology, and showed that the expected 5-year survival was 64.9% (personal communication). Given that a 5-year survival of at least 50% is traditionally taken as the lowest acceptable result in the setting of cadaveric LT [
      • Bruix J.
      • Sherman M.
      • Llovet J.M.
      • Beaugrand M.
      • Lencioni R.
      • Burroughs A.K.
      • et al.
      Clinical management of hepatocellular carcinoma. Conclusions of the Barcelona 2000 EASL conference.
      ,
      • Llovet J.M.
      • Burroughs A.
      • Bruix J.
      Hepatocellular carcinoma.
      ], the minimum number of patients could be calculated using the following assumptions:
      • 5-year survival of 64.9% in group within the MC;
      • 5-year survival of 50% in group beyond the MC but within the EC proposal;
      • Bi-directional analysis;
      • Type I error rate alpha level of 5%;
      • Type II error rate beta level of 20%.
      Adopting these parameters, sample size calculations require at least 139 patients in each arm to perform an adequate evaluation. All negative results published so far from the comparison of these two independent arms could therefore be due to the lack of statistic power, instead of representing a true similarity between the groups. Additionally, it is pertinent to note that this number of cases is in theory the smallest number that can be used, because it uses the lowest acceptable results in the group beyond the MC (50% at 5 years). If the acceptable mortality rate at 5 years is higher, the sample size will increase. Coincidently, this variation from 64.9% to 50% represents a relative difference around 25%. This magnitude of change has been suggested as reasonable difference between outcomes that can be used in clinical sample size calculation without compound endpoints [
      • Moher D.
      • Dulberg C.S.
      • Wells G.A.
      Statistical power, sample size, and their reporting in randomized controlled trials.
      ].

      Evidence based medicine

      There are various systems ranking publications in order to propose recommendations according to the robustness of data available in a specific setting. The Oxford Center of Evidence-based Medicine, the Newcastle-Ottawa Group, and the GRADE Working Group are proposals that allow a comprehensive review of the current evidence [

      Centre for evidence-based medicine (Oxford, UK). <http://www.cebm.net> [accessed February 2011].

      ,

      Weels GA, Shea B, O’Connel D, Peterson J, Welch V, Losos M, et al. The Newcastle-Ottawa Scale (NOS) for assessing the quality of nonrandomized studies in meta-analyses. <http://ohri.ca/programs/clinical_epidemiology/oxford.asp> [accessed February 2011].

      ,
      • Guyatt G.H.
      • Oxman A.D.
      • Vist G.
      • Kunz R.
      • Falck-Ytter Y.
      • Alonso-Coello P.
      • et al.
      Rating quality of evidence and strength of recommendations GRADE: an emerging consensus on rating quality of evidence and strength of recommendations.
      ]. Regardless of the guide used, meta-analysis and randomised controlled trials are the highest levels of evidence. A fundamental concern related to meta-analysis is to include only studies that are comparable with regard to design, outcomes, and other epidemiological points [

      Higgins JPT, Green S, editors. Cochrane handbook of systematic reviews of interventions 4.2.6. (updated September 2006). In: The Cochrane Library, Issue 4, Chichester, UK: John Wiley and Sons, Ltd.; 2006.

      ]. Despite the fact that there are statistical tools to determine the degree of heterogeneity in papers selected for a meta-analysis [
      • Higgins J.P.
      • Thompson S.G.
      Quantifying heterogenicity in a meta-analysis.
      ], the Cochrane Handbook for Systematic Reviews of Interventions points out that the primary inclusion criterion for studies must be linked to clinical judgement related to the specific topic to be evaluated [

      Higgins JPT, Green S, editors. Cochrane handbook of systematic reviews of interventions 4.2.6. (updated September 2006). In: The Cochrane Library, Issue 4, Chichester, UK: John Wiley and Sons, Ltd.; 2006.

      ]. The analysis of the design characteristics of existing studies summarized in Table 1 suggests that there is too much heterogeneity to consider meta-analysis at the moment. Randomised controlled trials in the setting of potentially life-saving therapy such a LT are theoretically possible, but in practice likely very difficult to conduct. An alternate study design to validate any EC proposal might be based on:
      • Radiological assessment properly performed;
      • Prospective design;
      • Comparison between patients within the MC and beyond the MC but within the new proposal;
      • Overall survival as the primary endpoint [
        • Llovet J.M.
        • Di Bisceglie A.M.
        • Bruix J.
        • Kramer B.S.
        • Lencioni R.
        • Zhu A.X.
        • et al.
        Panel of experts in HCC – design clinical trials. Design and endpoints of clinical trials in hepatocellular carcinoma.
        ];
      • An estimated number of patients of at least 139 patients in each arm.
      Looking at the studies shown in Table 1, it is clear that some concerns persist. Only three series approach the study design described above [
      • Herrero J.I.
      • Sangro B.
      • Quiroga J.
      • Pardo F.
      • Herraiz M.
      • Cienfuegos J.A.
      • et al.
      Influence of tumor characteristics on the outcome of liver transplantation among patients with liver cirrhosis and hepatocellular carcinoma.
      ,
      • Yao F.Y.
      • Xiao L.
      • Bass N.M.
      • Kerlan R.
      • Ascher N.R.
      • Roberts J.P.
      Liver transplantation for hepatocellular carcinoma: validation of the UCSF-expanded criteria based on preoperative imaging.
      ,
      • Guiteau J.J.
      • Cotton R.T.
      • Washburn W.K.
      • Harper A.
      • O’Mahony C.A.
      • Sebastian A.
      • et al.
      An early regional experience with expansion of Milan criteria for liver transplant recipients.
      ], but even these have significant design flaws. Herrero et al. analyzed only 24 patients in the beyond MC group but within the Navarra criteria, and the study design and the precise radiological characteristics of tumors are not clearly described. Yao et al. reported their experience in 38 patients beyond the MC but within the UCSF criteria, but followed these patients for a median of only 26 months, and they did not report the overall survival between the groups, only recurrence-free survival. It is well accepted that the overall survival is the main important outcome in phase III clinical trials, including specifically recommendations regarding HCC [
      • Llovet J.M.
      • Di Bisceglie A.M.
      • Bruix J.
      • Kramer B.S.
      • Lencioni R.
      • Zhu A.X.
      • et al.
      Panel of experts in HCC – design clinical trials. Design and endpoints of clinical trials in hepatocellular carcinoma.
      ,
      • Bruix J.
      • Sherman M.
      • Llovet J.M.
      • Beaugrand M.
      • Lencioni R.
      • Burroughs A.K.
      • et al.
      Clinical management of hepatocellular carcinoma. Conclusions of the Barcelona 2000 EASL conference.
      ]. Finally, Guiteau et al. evaluated the results of a new proposal adopted in the UNOS Region 4 (single nodule up to 6 cm, up to three nodules up to 5 cm, and a cumulative tumor burden of 9 cm) in 82 cases. Despite the appropriate design of this study, its main limitation was the short follow up. This study only followed patients for 3 years.
      An alternative method to validate an EC proposal is to evaluate a large cohort of patients identifying factors associated with different durations of survival. Mazzaferro et al. [
      • Mazzaferro V.
      • Llovet J.M.
      • Miceli R.
      • Bhoori S.
      • Schiavo M.
      • Mariani L.
      • et al.
      Predicting survival after liver transplantation in patients with hepatocellular carcinoma beyond the Milan criteria: a retrospective, exploratory analysis.
      ] recently published an international retrospective exploratory analysis only including cases beyond the MC on the basis of explant assessment. Among the 1112 cases enrolled, the subset of patients who had tumors within the up-to-seven criteria (HCC’s with seven as the maximum score based on adding the diameter of the largest tumors to the total number of tumors), without microvascular invasion, achieved a 71.2% 5-year overall survival. Despite the fact that the inherent concerns already commented on, such as tumor size assessment on the explant rather than pre-transplant radiology, this study does improve our understanding of EC.

      Transplanting HCC-patients with tumors beyond the conventional criteria using preoperative techniques to fulfill more selective criteria on the basis of tumor number and size

      The term “down-staging” (DS) can be defined as the use of any sort of treatment prior to LT in patients who have tumors beyond the MC in order to reduce tumor stage to be eligible for LT. Majno et al. presented the first experience using DS in HCC-patients in 1997. In a retrospective study, they showed higher survival rates in HCC patients treated with trans-arterial chemoembolization (TACE) and who responded, than in those who did not respond to TACE. The cohort consisted of patients with HCC larger than 3 cm or more than three nodules [
      • Majno P.E.
      • Adan R.
      • Bismuth H.
      • Castaing D.
      • Ariche A.
      • Krissat J.
      • et al.
      Influence of preoperative transarterial lipiodol chemoembolization on resection and transplantation for hepatocellular carcinoma in patients with cirrhosis.
      ]. Subsequent studies that have been published on the use of DS in the setting of LT are summarized in Table 2 [
      • Graziadei I.W.
      • Sandmueller H.
      • Waldenberger P.
      • Koeinigsrainer A.
      • Nachbaur K.
      • Jaschke W.
      • et al.
      Chemoembolization followed by liver transplantation for hepatocellular carcinoma impedes tumor progression while on waiting list and leads to excellent outcome.
      ,
      • Yao F.Y.
      • Hirose H.
      • LaBerge J.M.
      • Daverne 3rd, T.J.
      • Bass N.M.
      • Kerlan Jr., R.K.
      • et al.
      A prospective study on downstaging of hepatocellular carcinoma prior to liver transplantation.
      ,
      • Ravaioli M.
      • Grazi G.L.
      • Piscaglia F.
      • Trevisani F.
      • Cescon M.
      • Ercolani G.
      • et al.
      Liver transplantation for hepatocellular carcinoma: results of down-staging in patients initially outside the Milan selection criteria.
      ,
      • Chapman W.C.
      • Doyle M.B.
      • Stuart J.E.
      • Vachharajani N.
      • Crippin J.F.
      • Anderson C.D.
      • et al.
      Outcomes of neoadjuvant transarterial chemoembolization to downstage hepatocellular carcinoma before liver transplantation.
      ,
      • Lewandowski R.J.
      • Kulik L.M.
      • Riaz A.
      • Senthilnathan S.
      • Mulcahy M.F.
      • Ryu R.K.
      • et al.
      A comparative analysis of transarterial downstaging for hepatocellular carcinoma: chemoembolization versus radioembolization.
      ,
      • De Luna W.
      • Sze D.Y.
      • Ahmed A.
      • Ha B.Y.
      • Ayoub W.
      • Keeffe E.B.
      • et al.
      Transarterial chemoinfusion for hepatocellular carcinoma as downstaging therapy and a bridge toward liver transplantation.
      ,
      • Barakat O.
      • Wood R.P.
      • Ozaki C.F.
      • Ankoma-Sey V.
      • Galati J.
      • Skolkin M.
      • et al.
      Morphological features of advanced hepatocellular carcinoma as a predictor of downstaging and liver transplantation: an intention-to-treat analysis.
      ,
      • Jang J.W.
      • You C.R.
      • Kim C.W.
      • Bae S.H.
      • Yoon S.K.
      • Yoo Y.K.
      • et al.
      Benefit of downstaging hepatocellular carcinoma in a liver transplantation population.
      ]. All the concerns already discussed in relation to EC can be applied to DS as well. In addition, there are other issues specifically related to DS that need to be taken into account.
      Table 2Results from studies evaluating expanded criteria for cadaveric liver transplantation for patients with cirrhosis and hepatocellular carcinoma.
      aDisease-free survival.
      DS, down-staging; LT, liver transplantation; MC, Milan criteria; TACE, transarterial chemoembolization; HCC, hepatocellular carcinoma; ITT, intention-to-treat; UCSF, University of California, San Francisco; RAFE, radiofrequency ablation; PEI, percutaneous ethanol injection; LDLT, living donor liver transplantation; AASLD, American Association for the Study of Liver Diseases; EASL, European Association for the Study of the Liver; ALTSG, American Liver Tumor Study Group (reference 43); TARE, transarterial radioembolization; TACI, transcatheter arterial chemoinfusion; TARE-Y90, transarterial radioembolization with Yttrium-90; TACL, transarterial chemo-lipiodolization; AFP, alpha-fetoprotein.

      Listing criteria

      Both macrovascular invasion and extrahepatic spread are well established strong predictors of poor patient survival because of an unacceptably high risk of recurrence. With the exception of the study published by Chapman et al. [
      • Chapman W.C.
      • Doyle M.B.
      • Stuart J.E.
      • Vachharajani N.
      • Crippin J.F.
      • Anderson C.D.
      • et al.
      Outcomes of neoadjuvant transarterial chemoembolization to downstage hepatocellular carcinoma before liver transplantation.
      ], all other studies on DS excluded patients who had either macrovascular invasion or poor tumor differentiation. Currently, the discussion regarding the entry criteria for DS is based on tumor number and size beyond the MC. However, there is very good evidence that features other than tumor size, such as the degree of differentiation and the presence of microvascular invasion are major predictors of outcomes, and that the likelihood of these characteristics being present increases with tumor size [
      • Jonas S.
      • Bechstein W.O.
      • Steinmüller T.
      • Hermann M.
      • Radke C.
      • Berg T.
      • et al.
      Vascular invasion and histopathologic grading determine outcome after liver transplantation for hepatocellular carcinoma in cirrhosis.
      ,
      • Pawlik T.M.
      • Delman K.A.
      • Vauthey J.N.
      • Nagorney D.M.
      • Ng I.O.
      • Yamaoka Y.
      • et al.
      Tumor size predicts vascular invasion and histologic grade: implications for selection of surgical treatment for hepatocellular carcinoma.
      ]. In Table 2, it can be noted that only two studies clearly describe the entry characteristics of the patients. The UCSF proposal included a single tumor up to 8 cm, up to five tumors none larger than 3 cm, and a cumulative maximum tumor diameter of 8 cm [
      • Yao F.Y.
      • Hirose H.
      • LaBerge J.M.
      • Daverne 3rd, T.J.
      • Bass N.M.
      • Kerlan Jr., R.K.
      • et al.
      A prospective study on downstaging of hepatocellular carcinoma prior to liver transplantation.
      ]. Forty-three out of the 61 patients had successful DS to within the MC and 41 cases underwent LT with a 4-year survival of 92%. In the Bologna study, the upper limits were a single nodule up to 8 cm, two nodules up to 5 cm, up to five nodules none larger than 4 cm, and a cumulative maximum tumor diameter of 12 cm [
      • Ravaioli M.
      • Grazi G.L.
      • Piscaglia F.
      • Trevisani F.
      • Cescon M.
      • Ercolani G.
      • et al.
      Liver transplantation for hepatocellular carcinoma: results of down-staging in patients initially outside the Milan selection criteria.
      ]. Forty-eight patients underwent DS to within the MC. This was associated with an alpha-fetoprotein (AFP) level lower than 400 ng/ml and the 32 cases who were submitted to LT had a 3-year survival of 71%. The clear documentation of upper tumor limits is of fundamental importance in the DS setting and the lack of this information in almost all published studies is a major deficiency in interpreting these studies.

      Down-staging technique

      The different techniques used to achieve DS include TACE [
      • Majno P.E.
      • Adan R.
      • Bismuth H.
      • Castaing D.
      • Ariche A.
      • Krissat J.
      • et al.
      Influence of preoperative transarterial lipiodol chemoembolization on resection and transplantation for hepatocellular carcinoma in patients with cirrhosis.
      ,
      • Graziadei I.W.
      • Sandmueller H.
      • Waldenberger P.
      • Koeinigsrainer A.
      • Nachbaur K.
      • Jaschke W.
      • et al.
      Chemoembolization followed by liver transplantation for hepatocellular carcinoma impedes tumor progression while on waiting list and leads to excellent outcome.
      ,
      • Yao F.Y.
      • Hirose H.
      • LaBerge J.M.
      • Daverne 3rd, T.J.
      • Bass N.M.
      • Kerlan Jr., R.K.
      • et al.
      A prospective study on downstaging of hepatocellular carcinoma prior to liver transplantation.
      ,
      • Ravaioli M.
      • Grazi G.L.
      • Piscaglia F.
      • Trevisani F.
      • Cescon M.
      • Ercolani G.
      • et al.
      Liver transplantation for hepatocellular carcinoma: results of down-staging in patients initially outside the Milan selection criteria.
      ,
      • Chapman W.C.
      • Doyle M.B.
      • Stuart J.E.
      • Vachharajani N.
      • Crippin J.F.
      • Anderson C.D.
      • et al.
      Outcomes of neoadjuvant transarterial chemoembolization to downstage hepatocellular carcinoma before liver transplantation.
      ,
      • Lewandowski R.J.
      • Kulik L.M.
      • Riaz A.
      • Senthilnathan S.
      • Mulcahy M.F.
      • Ryu R.K.
      • et al.
      A comparative analysis of transarterial downstaging for hepatocellular carcinoma: chemoembolization versus radioembolization.
      ,
      • Barakat O.
      • Wood R.P.
      • Ozaki C.F.
      • Ankoma-Sey V.
      • Galati J.
      • Skolkin M.
      • et al.
      Morphological features of advanced hepatocellular carcinoma as a predictor of downstaging and liver transplantation: an intention-to-treat analysis.
      ,
      • Jang J.W.
      • You C.R.
      • Kim C.W.
      • Bae S.H.
      • Yoon S.K.
      • Yoo Y.K.
      • et al.
      Benefit of downstaging hepatocellular carcinoma in a liver transplantation population.
      ], radiofrequency ablation [
      • Yao F.Y.
      • Hirose H.
      • LaBerge J.M.
      • Daverne 3rd, T.J.
      • Bass N.M.
      • Kerlan Jr., R.K.
      • et al.
      A prospective study on downstaging of hepatocellular carcinoma prior to liver transplantation.
      ,
      • Ravaioli M.
      • Grazi G.L.
      • Piscaglia F.
      • Trevisani F.
      • Cescon M.
      • Ercolani G.
      • et al.
      Liver transplantation for hepatocellular carcinoma: results of down-staging in patients initially outside the Milan selection criteria.
      ,
      • Barakat O.
      • Wood R.P.
      • Ozaki C.F.
      • Ankoma-Sey V.
      • Galati J.
      • Skolkin M.
      • et al.
      Morphological features of advanced hepatocellular carcinoma as a predictor of downstaging and liver transplantation: an intention-to-treat analysis.
      ], arterial chemo-infusion [
      • De Luna W.
      • Sze D.Y.
      • Ahmed A.
      • Ha B.Y.
      • Ayoub W.
      • Keeffe E.B.
      • et al.
      Transarterial chemoinfusion for hepatocellular carcinoma as downstaging therapy and a bridge toward liver transplantation.
      ], percutaneous ethanol injection [
      • Yao F.Y.
      • Hirose H.
      • LaBerge J.M.
      • Daverne 3rd, T.J.
      • Bass N.M.
      • Kerlan Jr., R.K.
      • et al.
      A prospective study on downstaging of hepatocellular carcinoma prior to liver transplantation.
      ,
      • Ravaioli M.
      • Grazi G.L.
      • Piscaglia F.
      • Trevisani F.
      • Cescon M.
      • Ercolani G.
      • et al.
      Liver transplantation for hepatocellular carcinoma: results of down-staging in patients initially outside the Milan selection criteria.
      ], resection [
      • Yao F.Y.
      • Hirose H.
      • LaBerge J.M.
      • Daverne 3rd, T.J.
      • Bass N.M.
      • Kerlan Jr., R.K.
      • et al.
      A prospective study on downstaging of hepatocellular carcinoma prior to liver transplantation.
      ,
      • Ravaioli M.
      • Grazi G.L.
      • Piscaglia F.
      • Trevisani F.
      • Cescon M.
      • Ercolani G.
      • et al.
      Liver transplantation for hepatocellular carcinoma: results of down-staging in patients initially outside the Milan selection criteria.
      ,
      • Barakat O.
      • Wood R.P.
      • Ozaki C.F.
      • Ankoma-Sey V.
      • Galati J.
      • Skolkin M.
      • et al.
      Morphological features of advanced hepatocellular carcinoma as a predictor of downstaging and liver transplantation: an intention-to-treat analysis.
      ], and radio embolization [
      • Lewandowski R.J.
      • Kulik L.M.
      • Riaz A.
      • Senthilnathan S.
      • Mulcahy M.F.
      • Ryu R.K.
      • et al.
      A comparative analysis of transarterial downstaging for hepatocellular carcinoma: chemoembolization versus radioembolization.
      ,
      • Barakat O.
      • Wood R.P.
      • Ozaki C.F.
      • Ankoma-Sey V.
      • Galati J.
      • Skolkin M.
      • et al.
      Morphological features of advanced hepatocellular carcinoma as a predictor of downstaging and liver transplantation: an intention-to-treat analysis.
      ]. The majority of the studies summarized in Table 2 evaluated DS adopting a combination of various treatment protocols, often simply using what was standard for that institution and particular patient characteristics.
      To date, there have been no external validation studies of any proposed DS alternatives. Given the heterogeneity of treatments used in DS, none of the studies can be considered definitive, and the results of all the studies must be interpreted cautiously.

      Down-staging efficacy assessment

      The response to DS treatment has to be based on radiological measurement of tumor characteristics. Some of the difficulties in accuracy of radiology have already been discussed. The Response Evaluation Criteria in Solid Tumors (RECIST) has been traditionally used to define response to DS [
      • Chapman W.C.
      • Doyle M.B.
      • Stuart J.E.
      • Vachharajani N.
      • Crippin J.F.
      • Anderson C.D.
      • et al.
      Outcomes of neoadjuvant transarterial chemoembolization to downstage hepatocellular carcinoma before liver transplantation.
      ]. However, the RECIST criteria may not be adequate in this scenario. RECIST considers only tumor diameter, and does not take into account the areas of necrosis or the assessment of viability of tumor [
      • Therasse P.
      • Arbuck S.G.
      • Eisenhauer E.A.
      • Wanders J.
      • Kaplan R.S.
      • Rubinstein L.
      • et al.
      New guidelines to evaluate the response to treatment in solid tumors.
      ]. The EASL HCC guidelines suggested that assessment of tumor response should consider only the area of viable tumor [
      • Lencioni R.
      • Llover J.M.
      Modified RECIST (mRECIST) assessment for hepatocellular carcinoma.
      ,
      • Forner A.
      • Ayuso C.
      • Varela M.
      • Rimola J.
      • Hessheimer A.J.
      • De Lope C.R.
      • et al.
      Evaluation of tumor response after locoregional therapies in hepatocellular carcinoma: are response evaluation criteria in solid tumors reliable?.
      ], defined by arterial enhancement on a radiological contrast study. Although this was also endorsed by the AASLD guidelines, many studies report only RECIST criteria [
      • Graziadei I.W.
      • Sandmueller H.
      • Waldenberger P.
      • Koeinigsrainer A.
      • Nachbaur K.
      • Jaschke W.
      • et al.
      Chemoembolization followed by liver transplantation for hepatocellular carcinoma impedes tumor progression while on waiting list and leads to excellent outcome.
      ,
      • Chapman W.C.
      • Doyle M.B.
      • Stuart J.E.
      • Vachharajani N.
      • Crippin J.F.
      • Anderson C.D.
      • et al.
      Outcomes of neoadjuvant transarterial chemoembolization to downstage hepatocellular carcinoma before liver transplantation.
      ,
      • De Luna W.
      • Sze D.Y.
      • Ahmed A.
      • Ha B.Y.
      • Ayoub W.
      • Keeffe E.B.
      • et al.
      Transarterial chemoinfusion for hepatocellular carcinoma as downstaging therapy and a bridge toward liver transplantation.
      ,
      • Jang J.W.
      • You C.R.
      • Kim C.W.
      • Bae S.H.
      • Yoon S.K.
      • Yoo Y.K.
      • et al.
      Benefit of downstaging hepatocellular carcinoma in a liver transplantation population.
      ].
      Moreover, it has recently been suggested that there should be a period of at least 3 months from the date on which the imaging study shows HCC to be within the MC after DS treatment before undertaking transplant [
      • Pomfret E.A.
      • Washburn K.
      • Wald C.
      • Nalesnik M.A.
      • Douglas D.
      • Russo M.
      • et al.
      Report of a national conference on liver allocation in patients with hepatocellular carcinoma in the United States.
      ]. This interval would help to identify tumors with unfavorable biology and, consequently, avoiding LT in HCC patients with more aggressive tumors who would not benefit from this procedure. This strategy has been described by several authors [
      • Yao F.Y.
      • Hirose H.
      • LaBerge J.M.
      • Daverne 3rd, T.J.
      • Bass N.M.
      • Kerlan Jr., R.K.
      • et al.
      A prospective study on downstaging of hepatocellular carcinoma prior to liver transplantation.
      ,
      • Ravaioli M.
      • Grazi G.L.
      • Piscaglia F.
      • Trevisani F.
      • Cescon M.
      • Ercolani G.
      • et al.
      Liver transplantation for hepatocellular carcinoma: results of down-staging in patients initially outside the Milan selection criteria.
      ,
      • Chapman W.C.
      • Doyle M.B.
      • Stuart J.E.
      • Vachharajani N.
      • Crippin J.F.
      • Anderson C.D.
      • et al.
      Outcomes of neoadjuvant transarterial chemoembolization to downstage hepatocellular carcinoma before liver transplantation.
      ], but its effect on outcomes has not been assessed in comparative studies.
      The best strategy to evaluate the use of DS in clinical practice would be to conduct a multicenter and prospective cohort study targeted at downstaging HCC to within MC, with a control arm initially within the MC, adopting a standard DS protocol, i.e., standard diagnostic and staging tests, the clear establishment of upper tumor limits, the use of a standard DS technique for all patients and standard follow-up. Finally, the criteria to de-list patients who had been successfully down-staged but thereafter progressed beyond the acceptable criteria, as well as whether these patients might be re-listed following additional treatment have to be defined. For the majority of the studies that describe DS, tumor progression beyond the proposed down-staged criteria excludes patients from transplantation. This restriction has been applied to extended criteria as well, i.e., progression beyond the limits of the extended criteria is a reason to de-list the patient. Additional parameters such as TACE responsiveness and AFP level on WL have been proposed as an alternative tool in this setting [
      • Otto G.
      • Herber S.
      • Heise M.
      • Lohse A.W.
      • Mönch C.
      • Bittinger F.
      • et al.
      Response to transarterial chemoembolization as a biological selection criteria for liver transplantation in hepatocellular carcinoma.
      ,
      • Millonig G.
      • Graziadei I.W.
      • Freund M.C.
      • Jaschke W.
      • Stadlmann S.
      • Ladurner R.
      • et al.
      Response to preoperative chemoembolization correlates with outcome after liver transplantation in patients with hepatocellular carcinoma.
      ,
      • Vibert E.
      • Azoulay D.
      • Hoti E.
      • Iacopinelli S.
      • Samuel D.
      • Salloum C.
      • et al.
      Progression of alphafetoprotein before liver transplantation for hepatocellular carcinoma in cirrhotic patients: a critical factor.
      ]. Nevertheless, there are no robust data, and further studies are once again warranted.

      Beyond tumor number and size

      Apart from morphological characteristics, a number of alternative factors have been described as markers of tumor aggressiveness and risk of recurrence. These include response to TACE [
      • Otto G.
      • Herber S.
      • Heise M.
      • Lohse A.W.
      • Mönch C.
      • Bittinger F.
      • et al.
      Response to transarterial chemoembolization as a biological selection criteria for liver transplantation in hepatocellular carcinoma.
      ,
      • Millonig G.
      • Graziadei I.W.
      • Freund M.C.
      • Jaschke W.
      • Stadlmann S.
      • Ladurner R.
      • et al.
      Response to preoperative chemoembolization correlates with outcome after liver transplantation in patients with hepatocellular carcinoma.
      ], the degree of differentiation [
      • Kneteman N.M.
      • Oberholzer J.
      • Saghier M.A.
      • Meeberg G.A.
      • Blitz M.
      • Ma M.M.
      • et al.
      Sirolimus-based immunosuppression for liver transplantation in the presence of extended criteria for hepatocellular carcinoma.
      ,
      • Cillo U.
      • Vitale A.
      • Bassanello M.
      • Boccagni P.
      • Brolese A.
      • Zanus G.
      • et al.
      Liver transplantation for the treatment of moderately or well-differentiated hepatocellular carcinoma.
      ,
      • Cillo U.
      • Vitale A.
      • Grigoletto F.
      • Gringeri E.
      • D’Amico F.
      • Valmasoni M.
      • et al.
      Intention-to-treat analysis of liver transplantation in selected, aggressively treated HCC patients exceeding the Milan criteria.
      ], the gene-expression profile [
      • Hoshida Y.
      • Villanueva A.
      • Kobayashi M.
      • Peix J.
      • Chiang D.T.
      • Camargo A.
      • et al.
      Gene expressions in fixed tissues and outcome in hepatocellular carcinoma.
      ,
      • Lee J.S.
      • Shu I.S.
      • Heo J.
      • Calvisi D.F.
      • Sun Z.
      • Roskams T.
      • et al.
      Classification and prediction of survival in hepatocellular carcinoma by gene expression profiling.
      ,
      • Schwartz M.
      • Dvorchik I.
      • Roayaie S.
      • Fiel I.
      • Finkelstein S.
      • Marsh W.
      • et al.
      Liver transplantation for hepatocellular carcinoma: extension of indications based on molecular markers.
      ], the presence of microvascular invasion [
      • Shirabe K.
      • Itoh S.
      • Yoshizumi T.
      • Soegima Y.
      • Taketomi A.
      • Aishima S.
      • et al.
      The predictors of microvascular invasion in candidates for liver transplantation with hepatocellular carcinoma – with special reference to the serum levels of des-gamma-carboxy prothrombin.
      ], and the AFP levels [
      • Vibert E.
      • Azoulay D.
      • Hoti E.
      • Iacopinelli S.
      • Samuel D.
      • Salloum C.
      • et al.
      Progression of alphafetoprotein before liver transplantation for hepatocellular carcinoma in cirrhotic patients: a critical factor.
      ,
      • Jonas S.
      • Bechstein W.O.
      • Steinmmuler T.
      • Herrmann M.
      • Radke C.
      • Berg T.
      • et al.
      Vascular invasion and histopathologic grading determine after liver transplantation for hepatocellular carcinoma in cirrhosis.
      ,
      • Sotiropoulos G.C.
      • Malagó M.
      • Bockhorn M.
      • Schmitz K.J.
      • Radtke A.
      • Molmenti E.P.
      • et al.
      Liver transplantation for hepatocellular carcinoma and cirrhosis in candidates with undetectable or very low alpha-fetoprotein levels: is an expansion of listing criteria justified?.
      ,
      • Zheng S.S.
      • Xu X.
      • Wu J.
      • Chen J.
      • Wang W.L.
      • Zhang M.
      • et al.
      Liver transplantation for hepatocellular carcinoma: Hangzhou experiences.
      ].

      Treatment responsiveness

      Otto et al. [
      • Otto G.
      • Herber S.
      • Heise M.
      • Lohse A.W.
      • Mönch C.
      • Bittinger F.
      • et al.
      Response to transarterial chemoembolization as a biological selection criteria for liver transplantation in hepatocellular carcinoma.
      ] performed TACE in 96 HCC-patients to evaluate the impact of TACE-responsiveness on outcome post-LT. Sixty-two out of 96 patients had tumors beyond the MC before undergoing the initial TACE. Patients meeting the MC were immediately placed on WL, whereas cases beyond the MC were included on WL only after achieving at least a partial response by RECIST criteria (30% decrease in the sum of the largest diameter of five target lesions, taking as reference the baseline sum of the largest diameter). Fifty patients finally underwent LT, of whom 34 were in the group beyond the MC. The 5-year recurrence-free survival was similar in patients within and beyond the MC who responded to TACE, (93% vs. 74%, p= 0.42). When all transplanted patients were considered (n = 50), TACE-responsiveness was associated with improved patient survival, whereas survival was not related to whether the patients were within or beyond MC. However, the small sample size again makes these results hard to interpret.
      Millonig et al. [
      • Millonig G.
      • Graziadei I.W.
      • Freund M.C.
      • Jaschke W.
      • Stadlmann S.
      • Ladurner R.
      • et al.
      Response to preoperative chemoembolization correlates with outcome after liver transplantation in patients with hepatocellular carcinoma.
      ] published their experience using TACE in 116 HCC-patients in order to avoid tumor dropout beyond the UCSF criteria. One hundred and six out of the 116 cases enrolled underwent LT. According to the modified-RECIST criteria proposed in the 2001 EASL guidelines [
      • Bruix J.
      • Sherman M.
      • Llovet J.M.
      • Beaugrand M.
      • Lencioni R.
      • Burroughs A.K.
      • et al.
      Clinical management of hepatocellular carcinoma. Conclusions of the Barcelona 2000 EASL conference.
      ], patients with partial response (devascularisation of at least 30%) or complete response (no viable tumor) had better 5-year survival rates than patients who did not respond to TACE (62%, 93%, and 19%, respectively, p<0.001). However, in contrast to previous results, the subgroup analysis revealed that the usefulness of TACE-responsiveness was only associated with patients who were initially staged as having tumors within the MC, not the UCSF criteria. These data have to be confirmed in properly designed studies, but they do indicate that biologic characteristics such as response to treatment may be in the future incorporated into the selection criteria in HCC-patients for LT.

      Degree of differentiation

      In 2004, Cillo et al. [
      • Cillo U.
      • Vitale A.
      • Bassanello M.
      • Boccagni P.
      • Brolese A.
      • Zanus G.
      • et al.
      Liver transplantation for the treatment of moderately or well-differentiated hepatocellular carcinoma.
      ] evaluated the results of LT in 48 patients who did not have poorly differentiated tumors on biopsy performed pre-LT. They found a 5-year survival rate of 75%, independent of the number or size of the lesions. Recently, the same group updated their experience [
      • Cillo U.
      • Vitale A.
      • Grigoletto F.
      • Gringeri E.
      • D’Amico F.
      • Valmasoni M.
      • et al.
      Intention-to-treat analysis of liver transplantation in selected, aggressively treated HCC patients exceeding the Milan criteria.
      ], evaluating their results on the basis of the ITT principle, and comparing the survival rates between the cases within (n = 60) and beyond (n = 40) the MC, still considering only cases with moderately or well differentiated tumors. There was no significant difference in the 5-year survival between the groups (69% vs. 79%, respectively). Using a similar strategy, Kneteman et al. [
      • Kneteman N.M.
      • Oberholzer J.
      • Saghier M.A.
      • Meeberg G.A.
      • Blitz M.
      • Ma M.M.
      • et al.
      Sirolimus-based immunosuppression for liver transplantation in the presence of extended criteria for hepatocellular carcinoma.
      ] also showed the results of excluding cases with tumors larger than 5 cm with a poor degree of differentiation on biopsy prior to LT. The feasibility of adopting this approach to clinical practice has been challenged since biopsy samples may be misleading [
      • Pawlik T.M.
      • Gleisner A.L.
      • Anders R.A.
      • Assumpcao L.
      • Maley W.
      • Choti M.A.
      Preoperative assessment of hepatocellular carcinoma tumor grade using needle biopsy, implications for transplant eligibility.
      ]. HCC is notoriously heterogeneous histologically, and a biopsy may easily miss the areas of poor differentiation, resulting in a misclassification of the lesion as moderately or well differentiated.

      Gene-expression profile

      Recently, the role of genetic markers in HCC has come under scrutiny [
      • Hoshida Y.
      • Villanueva A.
      • Kobayashi M.
      • Peix J.
      • Chiang D.T.
      • Camargo A.
      • et al.
      Gene expressions in fixed tissues and outcome in hepatocellular carcinoma.
      ,
      • Lee J.S.
      • Shu I.S.
      • Heo J.
      • Calvisi D.F.
      • Sun Z.
      • Roskams T.
      • et al.
      Classification and prediction of survival in hepatocellular carcinoma by gene expression profiling.
      ,
      • Schwartz M.
      • Dvorchik I.
      • Roayaie S.
      • Fiel I.
      • Finkelstein S.
      • Marsh W.
      • et al.
      Liver transplantation for hepatocellular carcinoma: extension of indications based on molecular markers.
      ]. In the specific setting of LT for HCC, little is known. Schwartz et al. described a technique for detecting the allelic imbalance near tumor oncogene loci as an attempt to define molecular markers predictive of HCC recurrence after LT [
      • Schwartz M.
      • Dvorchik I.
      • Roayaie S.
      • Fiel I.
      • Finkelstein S.
      • Marsh W.
      • et al.
      Liver transplantation for hepatocellular carcinoma: extension of indications based on molecular markers.
      ]. Seventy HCC-patients who underwent LT were evaluated (35 within the MC and 35 beyond the MC). Twenty-four out of the 70 patients (34%) developed tumor recurrence after a median follow-up of 12.5 months. Allelic imbalance was significantly associated with recurrence for nine out of the 18 satellites studied. The cases who developed tumor recurrence after LT had significantly higher fractional allelic imbalance with a cut off of 0.27 (75% vs. 5%, respectively) regardless of whether the tumor was within or beyond the MC. Importantly, this study was performed on the analysis of explants characteristics. Thus, these findings should be still validated through the sample obtained from biopsies before LT.

      Microvascular invasion

      It is well-known that microvascular invasion is associated with worse survival and an increased risk of recurrence post LT [
      • Llovet J.M.
      • Di Bisceglie A.M.
      • Bruix J.
      • Kramer B.S.
      • Lencioni R.
      • Zhu A.X.
      • et al.
      Panel of experts in HCC – design clinical trials. Design and endpoints of clinical trials in hepatocellular carcinoma.
      ,
      • Bruix J.
      • Sherman M.
      • Llovet J.M.
      • Beaugrand M.
      • Lencioni R.
      • Burroughs A.K.
      • et al.
      Clinical management of hepatocellular carcinoma. Conclusions of the Barcelona 2000 EASL conference.
      ]. Despite some promising attempts to identify microvascular invasion before LT through imaging modalities [
      • Kornberg A.
      • Freesmeyer M.
      • Barthel K.
      • Jandt K.
      • Katenkamp K.
      • Steenbeck J.
      • et al.
      18F-FDG uptake of hepatocellular carcinoma on PET predicts microvascular tumor invasion in liver transplant patients.
      ,
      • Sumie S.
      • Kuromatsu R.
      • Okuda K.
      • Ando E.
      • Takata A.
      • Fukushima M.
      • et al.
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      ], to date there is no reliable way to identify microvascular invasion pre-LT. Consequently, attempts to identify pre-LT markers associated with microvascular invasion are now being investigated. Shirabe et al. measured des-gamma-carboxy-prothrombin (DCP) in the serum of patients with HCC in the non-transplant setting and found a correlation between an increased concentration of this marker and the presence of microvascular invasion, with a relatively high specificity of 85%. This finding has been confirmed by Koike et al. who, in addition, demonstrated that DCP level was the strongest predictive factor that correlated with the late development of tumor recurrence following treatment based on various forms of percutaneous ablation [
      • Keike Y.
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      ]. The usefulness of DCP as a reliable parameter associated with microvascular invasion has been suggested mostly in Japanese studies. Therefore, an international multicenter validation is required to assess the predictive value of this parameter.

      Alpha-fetoprotein levels

      Recently, some investigators have proposed that AFP values might play a role in selecting HCC-patients for LT [
      • Toso C.
      • Asthana S.
      • Bigam D.L.
      • Shapiro M.J.
      • Kneteman N.M.
      Reassessing selection criteria prior to liver transplantation for hepatocellular carcinoma utilizing the scientific registry of transplant recipients database.
      ,
      • Jonas S.
      • Bechstein W.O.
      • Steinmmuler T.
      • Herrmann M.
      • Radke C.
      • Berg T.
      • et al.
      Vascular invasion and histopathologic grading determine after liver transplantation for hepatocellular carcinoma in cirrhosis.
      ,
      • Sotiropoulos G.C.
      • Malagó M.
      • Bockhorn M.
      • Schmitz K.J.
      • Radtke A.
      • Molmenti E.P.
      • et al.
      Liver transplantation for hepatocellular carcinoma and cirrhosis in candidates with undetectable or very low alpha-fetoprotein levels: is an expansion of listing criteria justified?.
      ,
      • Zheng S.S.
      • Xu X.
      • Wu J.
      • Chen J.
      • Wang W.L.
      • Zhang M.
      • et al.
      Liver transplantation for hepatocellular carcinoma: Hangzhou experiences.
      ]. Once again, in the non-transplant setting, an elevated AFP is a marker of more advanced disease. An increase in AFP concentration might reflect tumor aggressiveness including differentiation degree and vascular invasion and, consequently lead to a higher risk of tumor recurrence. Toso et al. performed an overview of adult recipients in the Scientific Registry of Transplant Recipients from March 2002 to January 2008 [
      • Toso C.
      • Asthana S.
      • Bigam D.L.
      • Shapiro M.J.
      • Kneteman N.M.
      Reassessing selection criteria prior to liver transplantation for hepatocellular carcinoma utilizing the scientific registry of transplant recipients database.
      ]. Among the enrolled patients, 6268 had tumors within the MC on the basis of radiology. In the multivariate analysis, it was shown that high AFP levels and TTV >115 cm3 were associated with poor long-term survival. The 480 patients who presented with either TTV >115 cm3 (n = 13) or AFP >400 ng/ml had a 3-year survival lower than 50%. The progression of AFP levels while on WL has also been addressed [
      • Vibert E.
      • Azoulay D.
      • Hoti E.
      • Iacopinelli S.
      • Samuel D.
      • Salloum C.
      • et al.
      Progression of alphafetoprotein before liver transplantation for hepatocellular carcinoma in cirrhotic patients: a critical factor.
      ]. Using receiver operating characteristics curve analysis for recurrence after LT, Vibert et al. showed that 16% of HCC-patients who had an AFP increase >15 ng/ml per month while on WL (n = 26) had worse post transplant survival that those in whom the AFP rise was absent or less than 15 ng/ml/month. The authors concluded that the AFP progression during the WL could be incorporated as a preoperative marker of tumor aggressiveness.
      The above strategies involving markers of tumor biology all require additional validation. Nevertheless, it is clear that other parameters beyond tumor size and number are important, and should play a role in the selection of HCC patients for LT.

      Conclusions

      Given that untreated HCC-patients diagnosed at early stages have a 5-year survival of approximately 20% [
      • Llovet J.M.
      • Bustamante J.
      • Castells A.
      • Vilana R.
      • Ayuso M.delC.
      • Sala M.
      • et al.
      Natural history of untreated nonsurgical hepatocellular carcinoma: rationale for the design and evaluation of therapeutic trials.
      ], it is clear that both EC and DS provide benefit for individual patients, when compared to no therapy. Whereas with other cancer treatments, this degree of success would result in a change in practice, liver transplant cannot be considered in the same way. The persistent severe shortage of donor organs means that the importance of deriving maximum benefit from this valuable community resource has to be taken into account. Recently, Volk et al. showed that the adoption of more liberal criteria would lead to an increase of 44% risk of death among all patients on the WL (not just the HCC patients) [
      • Volk M.L.
      • Vijan S.
      • Marrero J.A.
      A novel model measuring of transplanting hepatocellular carcinoma exceeding Milan criteria.
      ]. In addition, it was estimated that a higher threshold of 61% 5-year survival is necessary to justify the use of a more liberal approach for listing HCC-patients beyond the MC at least in specific regions of the United States with severe organ shortage. The possibility of adopting more liberal selection criteria for HCC patients poses a dilemma. The acceptance of a more liberal organ allocation policy may result in denying the use of these organs to other patients for whom better results may be achieved. On the other hand, not accepting these criteria condemns individuals to non-curative therapies and denies them a treatment which may prolong their survival. This dilemma clearly demonstrates the importance of further, well designed studies that may overcome this paramount issue.

      Conflict of interest

      The authors declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.

      Acknowledgment

      The authors thank Dr. Mathias Bressel from the Mac Callum Cancer Institute of Melbourne for his comments on biostatistical issues.

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