HB patients who underwent LT in RJ-SJTUM between April 2016 and August 2022 (n = 44, female n = 23, male n = 21) were included in the detailed analysis based on their clinical information, with follow-up until October 31, 2023, or date of death. The inclusion criteria for our study were as follows: (1) patients diagnosed with hepatoblastoma based on clinical manifestations, laboratory examinations, and pathological examinations; (2) patients who received LT during the treatment process; and (3) patients who received LT for indications other than tumor treatment, such as liver failure or surgical complications after liver resection were excluded.

Clinical information of all HB patients who underwent LT in Mainland China from January 2019 to December 2022 was collected from the China Liver Transplant Registry (CLTR).

The study protocol was approved by the Ethics Committee of RJ-SJTUM (KY2020-055). Written informed consent was obtained from all enrolled patients or their parents. All aspects of the study complied with the Declaration of Helsinki and Istanbul, and there was no unethical practice used in this study.

After adequate neoadjuvant chemotherapy, LT will be considered when the patient meets any of the following criteria, otherwise hepatectomy will be considered: (1) POST-TEXT stage IV; (2) Tumor lesions involving three main branches of the hepatic veins (left hepatic vein, middle hepatic vein, right hepatic vein) or the inferior vena cava; (3) Tumor lesions involving two main branches of the portal vein (left portal vein, right portal vein) or the main trunk of the portal vein; (4) Postoperative residual liver volume less than 20% of the standard liver volume.

All data for the clinical variables were systematically collected from our prospectively maintained database. Demographic information and clinical characteristics of all patients, including age, sex, AFP level, hepatic vein/inferior vena cava invasion, portal vein invasion, extrahepatic disease contiguous with the main liver tumor, multifocal liver tumor, tumor rupture at diagnosis, and distal metastasis, were collected before the LT operation (13).

Primary liver transplantation (PLT) was planned and performed in patients with unresectable tumor lesions, including tumors with multifocal lesions or major vessel involvement. Salvage liver transplantation (SLT) was defined as LT performed in patients with HB recurrence after previous LRs, indicating that the true indication for listing patients for SLT was HB recurrence rather than other indications such as biliary/portal vein complications or liver failure. For patients with major vessel involvement, a whole-liver graft was preferred to replace the involved vessels. Pre-LT chemotherapy was administered to all the patients who underwent PLT. For patients listed for SLT after LR, pre-LT chemotherapy was administered during the waiting period to prevent tumor progression. Liver transplantation was performed for curative purposes; therefore, the metastases were completely eliminated or inactivated by chemotherapy or surgery before transplantation (14). No organs from the executed patients were transplanted or included in this study.

After LT, patient follow-up included clinical parameter tests (white blood cell count, hemoglobin, platelets, albumin, alanine aminotransferase, aspartate aminotransferase, total bilirubin, creatinine, INR) every 1 week during the first three months and every month later, AFP level every three months, ultrasound tests every three months during the first year, and every six months thereafter.

All patients who underwent LT were treated with our center's standardized post-transplant immunosuppressive therapy including tacrolimus/cyclosporin, mycophenolate, and prednisone. The doses were adjusted according to serum drug concentrations and liver function assays. Glucocorticoids were discontinued within one month after LT. In the last 5 years, sirolimus was started as a part of the immunosuppression regimen approximately one month after LT for most patients.

For persistent abnormal liver function after regular adjustment for immunosuppression therapy, pathological evaluation using core-needle liver biopsy was performed to confirm the diagnosis of rejection, liver injury, or viral infection.

Using our prospectively collected database, we analyzed patient outcomes during the current follow-up period. OS and PFS were calculated from the time of LT surgery. The survival rates of the different groups were compared using the log-rank test. Receiver operating characteristic (ROC) curves were constructed for continuous variables such as patient age, graft-to-recipient weight ratio (GRWR), intraoperative blood loss, and AFP before LT. Only the last were closely related to patient outcomes. AFP before LT was expressed as categorical variables using cut-off values. We chose the optimum cut-off to achieve the highest sum of specificity and sensitivity in the ROC curves. Univariate and multivariate Cox regression analyses were used to examine associations between patient demographics, clinical characteristics, OS, and PFS. In the multivariable Cox regression analysis, we included all factors with P ≤ 0.1 in the univariate analysis. The P values and hazard ratios (HR) of all factors in univariate Cox analysis were determined using the enter method, whereas the forward LR method was used in multivariate analysis. Unless otherwise stated, all analyses were performed with significance set at P < 0.05. Data collection and analysis were performed using SPSS 23.0 (Statistical Package for the Social Sciences, SPSS Inc., Chicago, IL, USA) and GraphPad Prism 8.4.0.

Between 2016 and 2022, 44 patients with HB underwent LT in RJ-SJTUM. The median follow-up duration was 35.0 (95% CI: 23.3–46.7) months. According to data from the CLTR (the official national liver transplant registry in Mainland China), between 2019 and 2022, 54 patients with HB underwent LT in Mainland China, of which 37 (68.5%) were from RJ-SJTUM (Figure 1A).

As mentioned above, Supplementary Table S1 summarized the patient and tumor characteristics of the RJ-SJTUM cohort. Notably, deceased donors were the key source for HB patients (77.3%) and the whole liver was the first choice (68.2%). Living-donor transplantation was not widely performed for HB in our cohort (22.7%). The OS rates at 1, 3, and 5 years after LT were 95.5%, 84.6%, and 84.6%, respectively, and the PFS rates at 1, 3, and 5 years were 63.6%, 63.6%, and 63.6% (Figure 1B). According to the CLTR follow-up data, the 3-year OS was 82.22% and the 5-year PFS was 63.64% in Mainland China.

We performed univariate and multivariate analyses in the LT cohort (n = 44) to identify the independent risk predictors of PFS after LT (Table 1). In univariate analysis, two factors were identified: patient with distal metastasis before LT (HR: 3.685, 95% CI: 1.269–10.705, P = 0.017) and patient with serum AFP ≥13,686.5 ng/ml before LT (after pre-transplantation chemotherapy) (HR: 6.825, 95% CI: 2.350–19.825, P < 0.001). In multivariate analysis, AFP ≥13,686.5 ng/ml before LT (HR: 6.825, 95% CI: 2.350–19.825, P < 0.001) was the only independent risk factor for PFS.

Survival analysis showed that PFS in HB patients with AFP <13,686.5 ng/ml was significantly higher than that in those with AFP ≥13,686.5 ng/ml (1/3/5 year OS: 82.8%/82.8%/82.8% vs. 26.7%/26.7%/-; P < 0.0001) (Figure 2A). As for OS, patients with AFP ≥13,686.5 ng/ml also showed poorer prognosis (1/3/5 year OS: 100.0%/96.4%/96.4% vs. 86.7%/61.9%/61.9%; P = 0.0191) (Figure 2B).

Similarly, we attempted to identify key predictors of OS in the LT cohort using univariate and multivariate analyses (Table 2). In univariate analysis, two factors were identified as credible candidates: distal metastasis before LT (HR, 8.246; 95% CI: 1.374–49.481, P = 0.021) and not using sirolimus (HR, 7.948; 95% CI: 0.872–72.436, P = 0.066). In multivariate analysis, distal metastasis before LT (HR, 7.513; 95% CI: 1.239–45.553, P = 0.028) was the only independent predictor of OS in HB patients who underwent LT.

We also compared the outcomes of patients without distal metastasis before LT vs. those with distal metastasis and found that the latter had significantly lower PFS (1/3/5 year OS: 70.3%/70.3%/70.3% vs. 28.6%/28.6%/-; P = 0.0103) (Figure 2C) and OS (1/3/5 year OS: 97.3%/94.4%/94.4% vs. 85.7%/42.9%/-; P = 0.0058) (Figure 2D).

We focused on clinical decision-making factors that were closely related to LT, including primary vs. salvage LT, graft type (whole liver vs. partial liver), donor type (living vs. deceased), and bile duct anastomosis (duct-to-duct vs. cholangioenteric). None of these factors affected PFS (Table 1) or OS (Table 2) in patients with HB who underwent LT.

Surgical complications occurred in three patients, including hepatic artery thrombosis (HAT) in two and biliary complications in one. One case of HAT occurred on the 1st day after LT, and the patient underwent a repeat surgery. The other case occurred on the 7th day after LT, and the patient received conservative treatment. Biliary stenosis occurred in one patient 1 month after LT. The patient underwent percutaneous transhepatic cholangial drainage (PTCD) and recovered 3 months later.

All the patients in our cohort received post-LT chemotherapy. Two patients had severe life-threatening liver injury caused by chemotoxicity. Notably, both patients were treated with ifosfamide, carboplatin, and etoposide (ICE) regimens. One patient recovered after eight months, and the other patient was listed for re-transplantation. In addition, one patient developed symptomatic Epstein-Barr virus infection.

Although we administered relatively mild immunosuppressive regimens to prevent tumor recurrence, we did not detect any severe graft rejection events that required liver biopsy in our cohort.

In our study, sixteen patients experienced tumor recurrence after LT, of which five died. All patients relapsed within 1 year after LT. Table 3 summarized the detailed demographics and tumor characteristics of these patients. The sites of recurrence were the lung in eleven patients, the liver in three patients, the lung/brain in one patient, and the lung/liver in one patient. Patients with localized tumor recurrence (mostly in the lung) had favorable prognoses with pulmonary surgeries to completely eliminate recurrent tumors. However, the prognosis of patients with diffuse tumor recurrence (in the liver, lung, and brain) is dismal.

mTOR inhibitors have been shown to be immunosuppressants with anti-tumor activity. In the last 5 years, we started using sirolimus one month after LT in all patients who could tolerate it. We compared the PFS and OS between patients treated with and without sirolimus after LT (Figures 3A,B). Although the results showed no statistical difference in PFS (Figure 3A), sirolimus appeared to prolong the OS (Figure 3B). We also found that of the five patients who died from tumor recurrence, four (80%) did not use sirolimus after LT. Interestingly, all eleven patients who survived tumor recurrence used sirolimus as a part of the immunosuppression regimen after LT (Table 3). Our results require further validation because of the short follow-up period and the small sample size. The relationship between sirolimus usage and HB patient prognosis after LT should be further explored in future studies, especially in patients with recurrence.