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Salvage Liver Transplantation for Recurrent Hepatocellular Carcinoma after Liver Resection: Retrospective Study of the Milan and Hangzhou Criteria

Background Salvage liver transplantation (SLT) has recently been proposed for recurrent hepatocellular carcinoma after liver resection; however, criteria for candidate assessment in SLT have not been thoroughly evaluated. Methods and Findings We retrospectively analyzed outcomes and factors affecting survival of 53 recipients who received SLT in the Liver Transplantation Center, The First Affiliated Hospital of Zhejiang University between 2004 and 2012. Thirty recipients fulfilled the Hangzhou criteria, of which 16 also fulfilled the Milan criteria, while the remaining 23 exceeded both criteria. The 1-year, 3-year and 5-year overall survival rates and tumor-free survival rates were both superior in patients fulfilling Milan or Hangzhou criteria compared with those exceeding the criteria. For recipients outside Milan criteria but within Hangzhou criteria, the 1-year, 3-year overall survival rates were 70.1%, 70.1%, similar to recipients within Milan criteria, with the 1-year, 3-year and 5-year overall survival of 93.8%%, 62.1% and 62.1% (P = 0.586). The tumor-free survival rates were also similar between these two subgroups, with 51.9% and 51.9% vs. 85.6%, 85.6% and 64.2% during the same time interval, respectively (P = 0.054). Cox regression analysis identified Hangzhou criteria (within vs. outside, hazard ratio (HR) 0.376) and diameter of the largest tumor (HR 3.523) to be independent predictors for overall survival. The only predictor for tumor-free survival was diameter of the largest tumor (HR 22.289). Conclusions Hangzhou criteria safely expanded the candidate pool and are feasible in assessment of candidates for SLT. This is helpful in donor liver allocation in transplant practice.


Introduction
Salvage liver transplantation (SLT) has recently been proposed for recurrent hepatocellular carcinoma (HCC) after previous liver resection [1,2]. The treatment procedure -which includes two steps, namely, first liver resection and subsequent liver transplantation -is very promising because it could greatly relieve the current burden due to increasingly long waiting lists and relatively limited organ resources. Previous studies have already showed comparable prognosis between recipients who underwent SLT and primary liver transplantation (PLT) [3,4]. The meta-analysis by Hu et al. assessed seven eligible studies reporting their experiences on SLT and observed that the overall survival rates as well as major post-transplant complications were similar between SLT and PLT [5].
Despite the encouraging observations in the field of SLT, confusion still exists. Traditionally, it has been widely accepted that SLT should be taken for recipients fulfilling Milan criteria [6] (namely, one lesion smaller than 5 cm or up to 3 lesions smaller than 3 cm) [7,8]. However, a study based on analysis of European Liver Transplant Registry indicated patients who recurred after a previous liver resection would often present with multiple tumor nodules, and only 25% fulfilled the Milan criteria [9]. This means nearly 75% of resected HCC patients who were initially transplantable would lose the opportunity for a secondary liver transplantation. Indeed, previous studies reported the transplantability of tumor recurrence was only 23% for SLT recipients [10]. So the Milan criteria seem too stringent with regard to SLT. Criteria are needed that ensure favorable prognosis while expanding the candidate pool to provide more patients access to SLT.
In a previous study, our center has proposed the Hangzhou criteria [11], which are as follows: patients without macrovascular invasion who have one of the two following items: (a) total tumor diameter less than or equal to 8 cm; (b) total tumor diameter more than 8 cm, simultaneously with histopathologic grade I or II and preoperative alpha fetoprotein (AFP) level less than or equal to 400 ng/mL. Recipients who met the Hangzhou criteria undergoing PLT could achieve survival rates comparable to those for recipients meeting the Milan criteria [12]. However, whether the Hangzhou criteria are applicable to SLT remains unknown. Our current study therefore analyzed data from the Liver Transplantation Center, The First Affiliated Hospital of Zhejiang University, to assess the feasibility of the Hangzhou criteria in their application to SLT. The Hangzhou criteria were indeed found feasible.

Ethics statement
Ethical approval was obtained from the Committee of Ethics in Biomedical Research of Zhejiang University. Written informed consent was obtained from all participants.

Study design
This is a single-center retrospective study approved by the Liver Transplant Center, The First Affiliated Hospital of Zhejiang University. All the data were from clinical records of the recipients.

Objectives
The aim of this study was to compare the feasibility of different recipient selection criteria in the setting of SLT.

Participants
Patients who received SLT between January 1, 2004 and December 31, 2012 in the Liver Transplant Center, The First Affiliated Hospital of Zhejiang University were included for analysis.
The inclusion criteria were: adult (.18 years old); Chinese nationality; HCC patients who underwent previous hepatectomy and received SLT because of tumor recurrence.
The exclusion criteria were: HCC patients who underwent previous hepatectomy and subsequent liver transplant without record of tumor recurrence (due to either liver failure or as de principle or bridge transplantation); recipients with other types of liver cancer (e.g., cholangiocarcinoma); loss to follow-up.
We finally included 53 recipients in this study. Of these, 45 were male and 8 were female. The mean age at transplantation was 48.0 6 8.2 years. Fourteen recipients received SLT before 2008, and 39 received SLT in 2008 or after. All the recipients had hepatitis B virus-associated HCC. The median Model for End-Stage Liver Disease (MELD) score was 9.0 (interquartile range 7 to 14). The detailed profiles and overall characteristics of recipients are depicted in Table 1.

Procedures
Recipients were classified based on whether they met the Milan criteria or Hangzhou criteria: 16 recipients met the Milan criteria and therefore also the Hangzhou criteria (MC group); 14 recipients exceeded the Milan criteria but still met the Hangzhou criteria (HZ group); the remaining 23 recipients exceeded the Hangzhou criteria and therefore also the Milan criteria.
The follow-up was routinely performed by the Liver Transplant Center, The First Affiliated Hospital of Zhejiang University. The tumor-recurrence surveillance strategy was in accordance with our previous literature [11]. Antiviral therapy for hepatitis B recurrence was based on lamivudine in combination with low-dose hepatitis B immunoglobulin (HBIG) schedules.
The following catalogued data were compared between the MC and HZ groups: age, gender, recipient blood type, blood type incompatibility, preoperative AFP level, MELD score, Tumor Node Metastasis (TNM) staging, Child-Pugh score, tumor number, diameter of the largest tumor, sum of tumor diameters, macrovascular invasion, cold ischemia time, warm ischemia time and intra-operative blood loss.
We analyzed the 1-year, 3-year and 5-year overall survival rates and tumor-free survival rates from the transplant date, and for each set of criteria (Milan or Hangzhou) compared these rates between recipients who met the criteria and recipients who exceeded them. Survival rates were further compared between the MC and HZ groups.

Statistical methods
Recipient characteristics were compared using the Mann-Whitney U test for continuous variables and Fisher's exact test for binomial variables where appropriate. Associations between recipient variables and survival were evaluated using univariate analysis. The variables analyzed in this study included gender (male or female), age (,50 or $50 years), recipient blood type (A, B, O or AB), donor-recipient blood type incompatibility (Y/N), transplant year (before 2008 or 2008 and after), MELD score (,15 or $15), Child-Pugh classification (A/B/C), TNM classification (I, II, III or IV), preoperative AFP level (#400 or .400 ng/mL), sum of tumor diameters (#8 or .8 cm), number of tumors (#3 or .3), diameter of the largest tumor (#5 or .5 cm), intra-operative blood loss (,2,500 or $2,500 mL), cold ischemia time (,9 or $9 h), warm ischemia time (,5 or $5 min), macrovascular invasion (with or without), Milan criteria (fulfilling and exceeding) and Hangzhou criteria (fulfilling and exceeding). And those with Pvalues less than 0.05 were further taken for the Cox regression analysis using a forward likelihood ratio test. Differences were considered statistically significant at a cutoff P-value of , 0.05; all tests were two-sided. All the analyses were performed using SPSS 16.0 (SPSS Inc, Chicago, IL).

Evaluation of Milan criteria and Hangzhou criteria
In a median follow-up of 16 months (interquartile range, 7.0 to 30.0 months) in all recipients, the 1-year, 3-year and 5-year overall survival rates were 71.7%, 38.6% and 38.6%, respectively, and the corresponding tumor-free survival rates were 62.9%, 51.3% and 42.8%.
Sixteen recipients met the Milan criteria, and 30 recipients met the Hangzhou criteria. Hangzhou criteria thus provided an expansion of 87.5% (N = 14).

Comparison of the MC and HZ groups
Comparison of patient profiles is depicted in Table 2. The sum of tumor diameters was significantly larger in the HZ group (median 6 cm vs. median 2 cm in the MC group). No significant differences were observed in the gender distribution, age, recipient blood type, blood type incompatibility, preoperative AFP level, MELD score, Child-Pugh score, TNM staging, tumor numbers, diameter of the largest tumor, macrovascular invasion, cold ischemia time, warm ischemia time and intro-operative blood loss between the MC and HZ groups.    The 1-year, 3-year and 5-year overall survival rates were 93.8%%, 62.1% and 62.1% in the MC group, and the 1-year, 3year overall survival rates were 70.1%, 70.1% in the HZ group. No significant difference was observed (P = 0.586, Figure 3A). Similarly no statistical difference was observed in the tumor-free survival rates, with 85.6%, 85.6% and 64.2% in the MC group compared with 51.9%, 51.9% in the HZ group during the same time interval (P = 0.054, Figure 3B).

Risk factors in univariate analysis
We then performed univariate analysis and identified macrovascular invasion, diameter of the largest tumor, Milan criteria and Hangzhou criteria as predictors for overall survival; and total tumor diameter, diameter of the largest tumor, Milan criteria and Hangzhou criteria as predictors for tumor-free survival ( Table 3 and Table S1).

Discussion
Liver transplantation has been accepted as the treatment of choice for HCC. With the introduction of the Milan criteria, which provided strict candidacy assessment, prognosis has greatly improved: 5-year overall survival exceeds 70%, and tumor recurrence rates are less than 10% [13]. However, many HCC patients would lose the opportunity for liver transplant because they exceed the Milan criteria, and also increasing evidence has been gained in some patients outside the Milan criteria. Under these circumstances, many transplant centers have been trying to expand the selection criteria to provide more HCC patients eligible for liver transplant. Proposals including the University of California, San Francisco (UCSF) criteria, up-to-seven criteria and Hangzhou criteria were established, all of which showed prognosis comparable to that fulfilling the Milan criteria [11,14,15].
However, donor liver shortage has restricted the wide application of liver transplant for HCC patients, and many patients would drop out of the waiting list because of tumor progression [16]. Prof. Bismuth first introduced SLT in 1999, and since then SLT has been accepted as a rational alternative way to delay tumor progression for HCC patients who are waiting for an available donor [2].
As in the case of PLT, we also faced the issue of candidate selection in SLT for recurrent HCC. Majno's group and Poon's group both proposed the Milan criteria as an assessment tool for recurrent HCC [7,8]. In this study, we observed that recipients with recurrent tumor characteristics within the Milan criteria could achieve significant superior overall and tumor-free survival rates to those for patients outside the Milan criteria, confirming their efficacy in assessment of eligible patients for SLT.
However, of the 53 patients who suffered from HCC recurrence in the current study, only 16 (30%) met the Milan criteria. Indeed, although patients would undergo close follow-up after liver resection, and recurrence would often be detected at an early stage, most of these recurrences would still be multifocal because of intra-hepatic dissemination from the primary tumor [7,17,18]. So patients would often present tumor morphology exceeding the Milan criteria [9]. The low transplantability somewhat conflicts with the primary purpose of SLT, which is supposed to benefit more recipients on the waiting list. So an extension of the boundaries of SLT for recurrent HCC needs to be considered.
Our previous study has shown recipients whose recurrent tumor fulfills the Hangzhou criteria and who receive SLT can achieve survival similar to that of recipients who undergo PLT within the Hangzhou criteria [3]. This indicates that to expand the candidate pool the Hangzhou criteria could potentially serve as selection criteria for SLT.
In the current study, we found that the overall and tumor-free survival rates were also significantly better in recipients fulfilling the Hangzhou criteria compared with those exceeding the Hangzhou criteria. Thirty out of the 53 recipients met the Hangzhou criteria, which included 14 more recipients for SLT compared with the Milan criteria, namely, 87.5% expansion in the candidate pool.
When further comparing recipients within the Milan criteria and recipients outside the Milan criteria but within the Hangzhou criteria, we observed that the sum of tumor diameters was significantly larger in the HZ group. Also the diameter of the largest tumor and the number of tumor nodules tended to be greater in the HZ group. Tumor gross features are important factors in recipient criteria. Burroughs et al performed a metaanalysis of 101 studies and concluded that the diameter of the largest tumor and total tumor volume were the best predictors for long-term prognosis [19]. The differences of tumor morphology between the MC and HZ groups partially reflects the expansion of tumor morphology in the Hangzhou criteria when selecting appropriate candidates. No survival differences existed between those two subgroups, which indicated the safe expansion of candidates by the Hangzhou criteria for SLT.
Moreover, the Hangzhou criteria were identified as one of the independent predictors for overall survival. As a matter of fact, unlike traditional recipient selection criteria, which mainly emphasize tumor morphology, the Hangzhou criteria take tumor differentiation grade and AFP into account. These two factors are mostly related to tumor biology. Recently, accumulated experience has been gained in the predictive role of tumor biology for prognosis in HCC patients. The study by Laurent's groups demonstrated that only histopathologic factors of the tumor were predictors for tumor recurrence after liver resection [20]. Also, the close relationship between preoperative AFP level and patient long-term survival in HCC patients has been increasingly recognized [21,22]. A recent study analyzing the Scientific Registry of Transplant Recipients (SRTR) suggested a combination of total tumor volume (cutoff at 115 cm 3 ) and preoperative AFP level (cutoff at 400 ng/mL) could most efficiently predict recipient survival [23]. Moreover, several papers have observed that most of the recurrences after liver resection have a more aggressive biological pattern as compared to primary tumors [17,24]. Combining these, there is an urgent need to take tumor biology into account when we select appropriate candidates for SLT, and the Hangzhou criteria feasibly evaluate prognosis in SLT candidates.
Based on our analysis, we propose that SLT is a feasible choice of treatment for patients with recurred tumor characteristics fulfilling the Hangzhou criteria. However, for those exceeding the Hangzhou criteria, SLT is not appropriate. Feasible treatment modalities including hepatectomy, interventional therapies (including TACE, RFA, etc.), molecular therapies, as well as directly to transplantation need to be further evaluated and discussed for those subpopulation patients. Moreover, it is important ot develop more accurate prediction algorithms based on meticulous evaluation of patient prognosis in the current liver transplant society, in order to maximally utilize the limited donor organ to benefit individual patient as well as the whole transplant population and achieve satisfactory prognosis.
Several limitations in our study need to be mentioned. Firstly, we lacked detailed information on tumor characteristics before liver resection, so we could not fully assess tumor characteristics in a particular patient at different time points. Secondly, our current study was limited by the small sample size, so we did not perform further subgroup analysis, results of which might be promising in guiding donor liver allocation in SLT. Moreover, the small sample size might also potentially affect the statistical analysis (for Table 3. Univariate analysis of variables related to post-liver transplantation survival (log-rank test) (P , 0.05 entered).

Overall survival rates
Tumor-free survival rates example, TNM classification, which was referred to as one of the most important factors reflecting prognosis, did not reach significant difference in our study, probably due to the small sample size). So our findings need to be further validated by welldesigned prospective multicenter studies with large sample size.
In conclusion, the Milan criteria are too stringent for SLT. The Hangzhou criteria safely expanded the number of candidates and are rational in assessing candidates for SLT. However, SLT was not appropriate for those patients exceeding the Hangzhou criteria. This is useful in guiding donor organ allocation in transplant practice.

Author Contributions
Conceived and designed the experiments: SZ ZH. Performed the experiments: JZ. Analyzed the data: ZL. Contributed reagents/materials/analysis tools: JX ZQ MZ. Wrote the paper: ZH JZ JW.