Liver transplantation for metastatic neuroendocrine tumors: Outcomes and prognostic variables

Factors Predicting Prognosis in Metastatic Grade 1 Gastro-entero-pancreatic Neuroendocrine Tumors

INTRODUCTION

The incidence of gastroenteropancreatic neuroendocrine tumors (GEP-NET) has steadily increased. These tumors are considered relatively indolent even when metastatic. What determines survival outcomes in such situations is understudied.

MATERIALS AND METHODS

Retrospective analysis of a prospectively maintained NET clinic database, to include patients of metastatic grade 1 GEP-NET, from January 2018 to December 2021, to assess factors affecting progression-free survival (PFS).

RESULTS

Of the 589 patients of GEP-NET treated during the study period, 100 were grade 1, with radiological evidence of distant metastasis. The median age was 50 years, with 67% being men. Of these, 15 patients were observed, while 85 patients received treatment in the form of surgery (n = 32), peptide receptor radionuclide therapy (n = 50), octreotide LAR (n = 22), and/or chemotherapy (n = 4), either as a single modality or multi-modality treatment. The median (PFS) was 54.5 months. The estimated 3-year PFS and 3-year overall survival rates were 72.3% (SE 0.048) and 93.4% (SE 0.026), respectively. On Cox regression, a high liver tumor burden was the only independent predictor of PFS (OR 3.443, p = 0.014). The 5-year OS of patients with concomitant extra-hepatic disease was significantly lower than that of patients with liver-limited disease (70.7% vs. 100%, p = 0.017).

CONCLUSION

A higher burden of liver disease is associated with shorter PFS in patients with metastatic grade I GEP-NETs. The OS is significantly lower in patients with associated extrahepatic involvement. These parameters may justify a more aggressive treatment approach in metastatic grade 1 GEP-NETs.

Liver transplantation as an alternative for the treatment of neuroendocrine liver metastasis: Appraisal of the current evidence

BACKGROUND

Liver transplantation (LT) for neuroendocrine liver metastases (NELM) is still in debate. Studies comparing LT with liver resection (LR) for NELM are scarce, as patient selection is heterogeneous and experience is limited. The goal of this review was to provide a critical analysis of the evidence on LT versus LR in the treatment of NELM.

DATA SOURCES

A scoping literature search on LT and LR for NELM was performed with PubMed, including English articles up to March 2023.

RESULTS

International guidelines recommend LR for NELM in resectable, well-differentiated tumors in the absence of extrahepatic metastatic disease with superior results of LR compared to systemic or liver-directed therapies. Advanced liver surgery has extended resectability criteria whilst entailing increased perioperative risk and short disease-free survival. In highly selected patients (based on the Milan criteria) with unresectable NELM, oncologic results of LT are promising. Prognostic factors include tumor biology (G1/G2) and burden, waiting time for LT, patient age and extrahepatic spread. Based on low-level evidence, LT for low-grade NELM within the Milan criteria resulted in improved disease-free survival and overall survival compared to LR. The benefits of LT were lost in patients beyond the Milan NELM-criteria.

CONCLUSIONS

With adherence to strict selection criteria especially tumor biology, LT for NELM is becoming a valuable option providing oncologic benefits compared to LR. Recent evidence suggests even stricter selection criteria with regard to tumor biology.

Transplant oncology - Current indications and strategies to advance the field

Liver transplantation (LT) was originally described by Starzl as a promising strategy to treat primary malignancies of the liver. Confronted with high recurrence rates, indications drifted towards non-oncologic liver diseases with LT finally evolving from a high-risk surgery to an almost routine surgical procedure. Continuously improving outcomes following LT and evolving oncological treatment strategies have driven renewed interest in transplant oncology. This is not only reflected by constant refinements to the criteria for LT in patients with HCC, but especially by efforts to expand indications to other primary and secondary liver malignancies. With new patient-centred oncological treatments on the rise and new technologies to expand the donor pool, the field has the chance to come full circle. In this review, we focus on the concept of transplant oncology, current indications, as well as technical and ethical aspects in the context of donor organs as precious resources.

Transplant Oncology: An Emerging Discipline of Cancer Treatment

Transplant oncology is an emerging concept of cancer treatment with a promising prospective outcome. The applications of oncology, transplant medicine, and surgery are the core of transplant oncology to improve patients' survival and quality of life. The main concept of transplant oncology is to radically cure cancer by removing the diseased organ and replacing it with a healthy one, aiming to improve the survival outcomes and quality of life of cancer patients. Subsequently, it seeks to expand the treatment options and research for hepatobiliary malignancies, which have seen significantly improved survival outcomes after the implementation of liver transplantation (LT). In the case of colorectal cancer (CRC) in the transplant setting, where the liver is the most common site of metastasis of patients who are considered to have unresectable disease, initial studies have shown improved survival for LT treatment compared to palliative therapy interventions. The indications of LT for hepatobiliary malignancies have been slowly expanded over the years beyond Milan criteria in a stepwise manner. However, the outcome improvements and overall patient survival are limited to the specifics of the setting and systematic intervention options. This review aims to illustrate the representative concepts and history of transplant oncology as an emerging discipline for the management of hepatobiliary malignancies, in addition to other emerging concepts, such as the uses of immunotherapy in a peri-transplant setting as well as the use of circulating tumor DNA (ctDNA) for surveillance post-transplantation.

The Role of Liver Transplantation in the Treatment of Liver Metastases from Neuroendocrine Tumors

OPINION STATEMENT

Transplant oncology is a new field of medicine referred to the use of solid organ transplantation, particularly the liver, to improve prognosis and quality of life in cancer patients. In unresectable, liver-only metastases from neuroendocrine tumors (NETs) of the digestive tract, liver transplantation represents a competitive chance of cure. Due to the limited resource of donated organs, accurate patients' selection is crucial in order to maximize transplant benefit. Several tumor- and patient-related factors should be considered. Among them, primary tumors with a low grade of differentiation (G1-G2 or Ki67 < 10%), located in a region drained by the portal system and removed before transplantation with at least 3-6 months period of disease stability observed before transplant listing, can be considered for transplantation. In case of NET located in the pancreas, extended lymphadenectomy should complement curative pancreatic resection. A number of other features are described in this review of liver transplantation for NET metastases. Comprehensive approach including various forms of non-surgical treatment and detailed planning and timing of total hepatectomy are discussed. Open issues remain on possible expansion of current criteria while maintaining the same long-term benefit demonstrated with the Milan NET criteria with respect to other non-transplant options, with particular reference to liver resection, peptide receptor radionuclide therapy, and locoregional and systemic treatments.

Long-Term Outcomes of Liver Transplantation for the Management of Neuroendocrine Neoplasms: A Systematic Review

Liver transplantation is an uncommonly used, controversially debated therapeutic approach for highly selected individuals with neuroendocrine liver metastases. Synthesising evidence regarding outcomes from this approach is crucial to understand its position within the broad neuroendocrine liver metastases armamentarium. In this narrative systematic review of studies published in PubMed, Scopus and OVID until 1 July 2021, we summarise and critically appraise the existing literature regarding this modality, with a special focus on long-term outcomes data where possible. Fourteen studies were identified that reported outcomes from the use of liver transplantation for metastatic neuroendocrine neoplasms. No randomised trials were identified. Generally, indications and selection criteria were poorly articulated, with the notable exception of studies using the Milan criteria. The median 5-year overall survival was 65% (ranging from 36% to 97.2%, 11 studies), and the median 10-year overall survival was 50% (ranging from 46.1% to 88.8%, 3 studies). One additional study focussed on treatments and outcomes following post-transplant recurrence. No studies reported outcomes past 10 years. Further follow-up of the largest series with explicit selection criteria will deepen our understanding of the role that transplantation has to play in this setting.

Liver Transplant for Patients With Neuroendocrine Tumor: A Report of 2 Exceptional Cases and Literature Review

Patients with neuroendocrine tumors with unresec-table liver involvement can benefit from liver transplant. There is a specific set of guidelines for neuroendocrine tumors with liver metastasis that involve less than 50% of the liver. However, beyond those guidelines, there are reports of exceptional criteria patients who benefited from liver transplant. Here, we present 2 unusual cases of patients with exceptional circumstances and with neuroendocrine tumors who underwent liver transplant. The first case describes a patient with an extremely rare neuroen-docrine tumor of the proximal common bile duct that caused liver biliary cirrhosis. The patient underwent tumor resection and liver transplant concurrently. The second case describes a patient with a neuroendocrine tumor of unknown primary origin with more than 50% hepatic involvement who received a liver transplant after downstaging. In our center, patients with unresectable hepatic metastases from neuroendoc-rine tumors are currently selected for liver transplant based on well-established criteria. However, these 2 cases did not meet the criteria for consideration of liver transplant; thus, multidisciplinary team sessions were held to discuss these 2 cases. After a period of nonsurgical treatment and evaluation of the tumor behavior, we selected the patients as candidates for liver transplant based on the favorable tumor behavior and favorable response to treatment. For both patients, we did not observe any signs of tumor recurrence during follow-up. The outcomes were acceptable, and the patients tolerated treatment well. Considering the favorable tumor pathology (G1 phase and low Ki67 index), we suggest that more studies should be conducted to evaluate the outcomes of patients with low-grade tumors and that the criteria for patients with low-grade tumors could be extended based on such future data.

Transplant oncology: multivisceral transplantation for neuroendocrine tumor and liver metastasis

PURPOSE OF REVIEW

Neuroendocrine tumor (NET) liver metastatic lesions are often multiple and found to be unresectable. Rationale of multivisceral transplantation (MVT: liver-pancreas-intestine transplantation) include radical and complete resection of primary, visible and invisible metastatic tumors by removing all abdominal organs and the lymphatic system. This review aims to describe the concept of MVT for NET and neuroendocrine liver metastasis (NELM), patient selection, timing of MVT, and posttransplant outcomes and management.

RECENT FINDINGS

Although indication criteria of MVT for NET vary between transplant centers, the Milan-NET criteria for liver transplant are often applied to MVT candidates. Extra-abdominal tumors such as lung and/or bone lesions should be ruled out prior to MVT. Histology should be confirmed as low-grade (G1/G2). Ki-67 should be also checked to confirm biologic features. Timing of MVT remains controversial, whereas many experts recommend 6 months of disease stability prior to MVT.

SUMMARY

Although MVT would not be a standard therapy because of limited access to MVT centers, benefit of MVT should be recognized, which includes its potential ability to better achieve curative resection of disseminated tumors in the abdominal cavity. Early referral of difficult cases to MVT centers should be considered before palliative best supportive cares.

Transplantation for metastatic liver disease

The liver is a common site of metastases from many cancers, particularly those originating in the gastrointestinal tract. Liver transplantation is an uncommonly used but promising and at times controversial treatment option for neuroendocrine and colorectal liver metastases. Transplantation with meticulous patient selection has been associated with excellent long-term outcomes in individuals with neuroendocrine liver metastases, but questions remain regarding the role of transplantation in those who could also be eligible for hepatectomy, the role of neoadjuvant/adjuvant treatments in minimising recurrence, and the optimal timing of the procedure. A prospective pilot study of liver transplantation for unresectable colorectal liver metastases that reported a 5-year overall survival rate of 60% reinvigorated interest in this area following initially dismal outcomes. This has been followed by larger studies, and prospective trials are ongoing to quantify the potential benefits of liver transplantation over palliative chemotherapy. This review provides a critical summary of currently available knowledge on liver transplantation for neuroendocrine and colorectal liver metastases, and highlights avenues for further study to address gaps in the evidence base.

Liver transplantation in gastroenteropancreatic neuroendocrine tumors

Neuroendocrine tumors are part of a heterogeneous group of tumors located in organs such as the gastrointestinal tract (GIT), lungs, thymus, thyroid, and adrenal glands. The most prevalent sites are the small intestine, cecal appendix, and pancreas. More than 50% of these tumors are associated with metastases at the time of diagnosis. Neuroendocrine tumors are classified according to the degree of cell differentiation and the histopathological proliferation index of the lesion. Neuroendocrine tumors can be well differentiated or poorly differentiated. G3 tumors are characterized by Ki-67 expression greater than 20% and can be either well differentiated (G3 NET) or poorly differentiated (G3 NEC). Neuroendocrine carcinoma (NEC G3) is subdivided into small-cell and large-cell types. When neuroendocrine tumors present clinical and compressive symptoms, carcinoid syndrome is evident. Carcinoid syndrome occurs when the tumor produces neuroendocrine mediators that cannot be metabolized by the liver due to either the size of the tumor or their secretion by the liver itself. Several therapeutic strategies have been described for the treatment of metastatic neuroendocrine tumors, including curative or palliative surgical approaches, peptide receptor radionuclide therapy, percutaneous therapy, systemic chemotherapy, and radiotherapy. Liver surgery is the only approach that can offer a cure for metastatic patients. Liver metastases must be completely resected, and in this context, orthotopic liver transplantation has gained prominence for yielding very promising outcomes in selected cases. The aim of this study is to review the literature on OLT as a form of treatment with curative intent for patients with gastroenteropancreatic neuroendocrine tumors with liver metastasis.

Where Are We Now with Liver Transplantation in Neuroendocrine Neoplasms? The Place of Liver Transplantation for Grades 1 and 2 Well-Differentiated Unresectable Liver Metastatic Neuroendocrine Tumours

PURPOSE OF REVIEW

This review outlines the role of liver transplantation in selected patients with unresectable neuroendocrine tumour liver metastases. It discusses the international consensus on eligibility criteria and outlines the efforts taking place in the UK and Ireland to develop effective national liver transplant programmes for neuroendocrine tumour patients.

RECENT FINDINGS

In the early history of liver transplantation, indications included cancer metastases to the liver as well as primaries of liver origin. Often, liver transplantation was a salvage procedure. The early results were disappointing, including in patients with neuroendocrine tumours. These data discouraged the widespread adoption of liver transplantation for neuroendocrine tumour liver metastases (NET LM). A few centres persisted in performing liver transplantation for patients with NET LM and in determining parameters predictive of good outcomes. Their work has provided evidence for benefit of liver transplantation in a selected group of patients with NET LM. Liver transplantation for NET LM is now accepted as a valid indication by many professional bodies, including the European Neuroendocrine Tumour Society (ENETS) and the United Network for Organ Sharing (UNOS). It is nevertheless rarely utilised. The UK and the Republic of Ireland are commencing a pilot programme of liver transplantation in selected patients. This programme will help develop the expertise and infrastructure to make liver transplantation for NET LM a routine procedure.

Overall Survival in Patients with Stage IV Pan-NET Eligible for Liver Transplantation

BACKGROUND

The use of liver transplantation (LT) in patients with stage IV neuroendocrine pancreatic tumors (pan-NET) is under debate. Previous studies report a 5-year survival of 27-53% after LT in pan-NET and up to 92.7% in patients with mixed NETs. This study aimed to determine survival rates of patients with stage IV pan-NET meeting criteria for LT while only subjected to multimodal treatment.

METHODS

Medical records of patients with pan-NET diagnosed from 2000 to 2021 at a tertiary referral center were evaluated for eligibility. Patients without liver metastases, who did not undergo primary tumor surgery, age > 75 years and with grade 3 tumors were excluded. The patients were divided into groups; all included patients, patients meeting the Milan, the United Network for Organ Sharing (UNOS) or the European Neuroendocrine Tumor Society (ENETS) criteria for LT. Kaplan-Meier survival analysis was used to calculate overall survival.

RESULTS

Out of 519 patients with pan-NET, 41 patients were included. Mean follow-up time was 5.4 years. Overall survival was 9.3 years (95% Cl 6.8-11.7), and 5-year survival was 64.7% (95% CI 48.2-81.2). Patients meeting the Milan, ENETS and UNOS criteria for LT had a 5-year survival of 64.9% (95% CI 32.2-97.6), 85.7% (95% CI 59.8-100.0) and 55.4% (95% CI 26.0-84.8), respectively.

CONCLUSIONS

In patients with stage IV pan-NET, grade 1 and 2, with no extra abdominal disease, 5-year survival was 64.7% (95% CI 48.2-81.2). As these survival rates exceed previously published series of LT for pan-NET, the evidence base for this treatment is very weak.

Treatment strategies for neuroendocrine liver metastases: a systematic review

BACKGROUND

Gastroenteropancreatic neuroendocrine tumors are often diagnosed when metastatic. The liver is the main site of metastases. Unfortunately, optimal management of neuroendocrine liver metastases remains a topic of debate. The aim of this study was to make a systematic review of the current literature about the results of the different treatments of neuroendocrine liver metastases.

METHODS

A systematic review was conducted for English language publications from 1995 to 2021. Outcomes were analyzed according to survival, disease-free survival, and in the case of systemic therapies, progression-free survival.

RESULTS

5509 patients were analyzed in the review. 67% of patients underwent surgery achieving 5 years overall survival despite only 30% percent without a recurrence. 60% of patients that had received a transplant reached 5 years survival with a low disease-free survival rate (20%). Five-year survival rate was 36.2% for patients undergoing loco-regional therapies.

CONCLUSION

Surgical resection is the best treatment when metastases are resectable, with the highest rate of survival, although liver transplantation shows good results for patients not eligible for surgery. Loco-regional therapies may be useful when surgical resection is contraindicated, or selectively used as a bridge to surgery or transplantation. Systemic therapies are indicated in patients for whom curative treatment cannot be obtained.

Effects of transplantation-related immunosuppression on co-existent neuroendocrine tumours

BACKGROUND

Here we detail our experience of managing patients found to have a neuroendocrine neoplasm (NEN) whilst on immunosuppression for a transplanted organ.

AIM

We aimed to quantify the behaviour of NENs under solid-organ transplant-related immunosuppression.

DESIGN

This was an observational, retrospective case series.

METHODS

Ten patients were identified from a prospectively kept database. Three were excluded.

RESULTS

Four patients received a liver, two a kidney, and one a heart transplant. All but one received calcineurin-based immunosuppression. NENs were found in five patients post-transplant: one had surgery for transverse colonic neuroendocrine carcinoma NEC (pT4N1M0, Ki67 60%), was cancer-free after four years; one had cold biopsy of duodenal NEN (pT1N0M0, Ki67 2%), cancer-free at four months; one 7 mm pancreatic NEN (pT1N0M0), untreated and stable for seven years; one small-bowel NEN with mesenteric metastasis (pTxNxM1), alive four years after diagnosis; and one untreated small-bowel NEN with mesenteric metastasis, stable at 1 year after liver transplantation. Two NENs were discovered pre-transplant, one pancreatic NEN (pT1N0M0, Ki67 5%), remains untreated and stable at three years. One gastric NEN (type 3, pT1bN0M0, Ki67 2%) remains stable without treatment for two years.

CONCLUSIONS

NENs demonstrate indolent behaviour in the presence of transplant-related immunosuppression.

Orchestrating Treatment Modalities in Metastatic Pancreatic Neuroendocrine Tumors-Need for a Conductor

Pancreatic neuroendocrine tumors (pNETs) are a vast growing disease. Over 50% of these tumors are recognized at advanced stages with lymph node, liver, or distant metastasis. An ongoing controversy is the role of surgery in the metastatic setting as dedicated systemic treatments have emerged recently and shown benefits in randomized trials. Today, liver surgery is an option for advanced pNETs if the tumor has a favorable prognosis, reflected by a low to moderate proliferation index (G1 and G2). Surgery in this well-selected population may prolong progression-free and overall survival. Optimal selection of a treatment plan for an individual patient should be considered in a multidisciplinary tumor board. However, while current guidelines offer a variety of modalities, there is so far only a limited focus on the right timing. Available data is based on small case series or retrospective analyses. The focus of this review is to highlight the right time-point for surgery in the setting of the multimodal treatment of an advanced pancreatic neuroendocrine tumor.

Postrecurrence Survival After Liver Transplantation for Liver Metastases From Neuroendocrine Tumors

BACKGROUND

Liver metastases from neuroendocrine tumors (NETs) is an accepted indication for liver transplantation (LT). Despite strict patient selection, post-LT recurrence is observed in 30-50% of cases. Postrecurrence survival is poorly investigated as well as factors influencing postrecurrence outcomes.

METHODS

Consecutive patients treated at a single Institution for post-LT recurrence of NET between Jan 1st, 2004 and Dec 31th, 2018 were included. Baseline patients' characteristics, data on the primary tumor, pretransplant therapies, posttransplant recurrence and treatments and long-term outcomes were prospectively collected and retrospectively analyzed.

RESULTS

Thirty-two patients presented with post-LT NET recurrence occurring 82.9 months (IQR 29.4-119.1) from LT, and the most common sites were abdominal lymph nodes (59.4%), peritoneum (6.3%) and lungs (6.3%). Fourteen patients (43.8%) underwent surgery with radical intent. Five- and 10-years survival after recurrence were 76.3% and 45.5%, respectively. Only time from LT to recurrence had a significant impact on post recurrence survival, being 5-years OS 89.5% versus 0% for patients recurring > 24 months after LT versus ≤ 24 months, respectively (p=.001). Moreover, for patients with Mib-1 > 2% at recurrence, 5-years OS was 87.5% versus 0% for those undergoing surgery versus loco-regional or systemic treatments (p=0.011).

CONCLUSIONS

The presented results, although based on a retrospective and relatively small series, show that excellent long-term survival is observed after post-LT NET recurrence, particularly in those patients recurring long after LT (> 24 months). An aggressive surgical treatment might result in a new chance of cure for a selected subgroup of patients.

Currently available treatment options for neuroendocrine liver metastases

Neuroendocrine neoplasms (NEN) are frequently characterized by a high propensity for metastasis to the liver, which appears to be a dominant site of distant-stage disease, affecting quality of life and overall survival. Liver surgery with the intention to cure is the treatment of choice for resectable neuroendocrine liver metastases (NELM), aiming to potentially prolong survival and ameliorate hormonal symptoms refractory to medical control. Surgical resection is indicated for patients with NELM from well-differentiated NEN, while its feasibility and complexity are largely dictated by the degree of liver involvement. As a result of advances in surgical techniques over the past decades, complex 1- and 2-stage, or repeat liver resections are performed safely and effectively by experienced surgeons. Furthermore, liver transplantation for the treatment of NELM should be anchored in a multimodal and multidisciplinary therapeutic strategy and restricted only to highly selected individual cases. A broad spectrum of interventional radiology treatments for NELM have recently been available, with expanding indications that are more applicable, as they are less limited by patient- and tumor-related parameters, being therefore important adjuncts or alternatives to surgery. Overall, liver-targeted treatment modalities may precede the administration of systemic molecular targeted agents and chemotherapy for patients with liver-dominant metastatic disease; these appear to be a crucial component of multimodal management of patients with NEN. In the present review, we discuss surgical and non-surgical liver-targeted treatment approaches for NELM, each complementing the other, with a view to assisting physicians in optimizing multimodal NEN patient care.

The Revolution in Indication for Liver Transplantation: Will Liver Metastatic Disease Overcome the End-Stage Liver Disease in the Next Future?

Indications for liver transplantation (LT) have constantly been evolving during the last few decades due to a better understanding of liver diseases and innovative therapies. Likewise, also the underlying causes of liver disease have changed. In the setting of transplant oncology, recent developments have pushed the boundaries of oncological indications for LT outside hepatocellular carcinoma (HCC), especially for secondary liver tumors, such as neuroendocrine and colorectal cancer. In the next years, as more evidence emerges, LT could become the standard treatment for well-selected metastatic liver tumors. In this manuscript, we review and summarize the available evidence for LT in liver tumors beyond HCC with a focus on metastatic liver malignancies, highlighting the importance of these new concepts for future implications.

Recent developments and ongoing trials in transplant oncology

Over the past two decades since the introduction of the Milan criteria, the field of transplant oncology has undergone a rapid development with a rising proportion of liver transplantations being performed for oncological indications. For many patients with liver tumours, transplantation represents the only chance for cure. However, many challenges remain, such as the adequate patient selection, management of post-transplant recurrence and refinement of neoadjuvant treatment protocols. This review provides an overview of the current state of the art of liver transplantation for oncological indications such as hepatocellular carcinoma, cholangiocarcinoma, colorectal liver metastasis and metastatic neuroendocrine tumours. We also summarize the ongoing research and explore future trends. Clinical trials are currently studying new diagnostic modalities, innovative pharmacological treatments, novel surgical techniques, downstaging regimens and new indications for liver transplantation. These emerging results will continue to shape the field of transplant oncology and provide us with the necessary tools to better select, treat and follow patients with liver tumours qualifying for liver transplantation.

Liver transplantation in the treatment of unresectable hepatic metastasis from neuroendocrine tumors

Neuroendocrine tumors (NET) are rare neoplasms with generally indolent growth behavior. The liver is the most common site of NET metastasis. The NET metastatic spread to the liver are usually multiple tumors involving bilateral hemilivers. For patients with isolated NET metastasis to the liver, a complete extirpation (R0) resection of both the primary NET and liver metastasis provide the best chance of tumor recurrence-free patient survival. Orthotopic liver transplantation (OLT) presents a viable treatment option for patients with unresectable liver metastasis from NET. Post-OLT outcomes for the patients of NET with liver metastasis (5-year overall survival rate 47-71%) are comparable to those for other indications. However, the high rate of recurrence after OLT (31-57%) remains a clinical obstacle. As such, it is imperative to consider each patient individually and identify prognostic factors that would impact post-OLT outcomes. This article focuses on the role of OLT in the definitive treatment of metastatic liver NET, review patient selection criteria predictive of survival outcomes and post-OLT outcomes for patients.

Liver transplantation for unresectable malignancies: Beyond hepatocellular carcinoma

Indications for liver transplantation have expanded over the past few decades owing to improved outcomes and better understanding of underlying pathologies. In particular, there has been a growing interest in the field of transplant oncology in recent years that has led to considerable developments which have pushed the boundaries of malignant indications for liver transplantation beyond hepatocellular carcinoma (HCC). In this article, we review and summarise the published evidence for liver transplantation in non-HCC primary and metastatic liver malignancies and highlight ongoing clinical trials that address unresolved questions therein. We also examine the current technical, immunological and oncological challenges that face liver transplantation in this growing field and explore potential approaches to overcome these barriers.

Liver transplantation in patients with liver metastases from neuroendocrine tumors

The prevalence of metastatic disease in neuroendocrine tumors (NETs) is very high (60-80%) and cancer-related death among these patients is generally due to metastatic disease. Numerous treatment options for cure and disease control have been investigated for patients with neuroendocrine liver metastases (NELM). Despite the success of liver directed therapy on slowing tumor progression and palliating symptoms, the chance of being cured by liver resection is 40-50% and only roughly 20% of patients have potentially resectable disease. As such, there has been interest in liver transplantation (LT) as a potentially curative option for patients with unresectable disease. Several criteria have been proposed in order to balance long-term outcomes of patients with NELM and the problem of organ shortage including the Milan-NET criteria, the UNOS criteria and the ENETS guidelines. In the most representative studies, recurrence rate after LT has ranged from 30% to 60% with a 5-year OS ranging from 50% to 97%. This large variability is due to the retrospective nature of the studies available, which used different inclusion criteria. As such, outcomes and the prognostic factors associated with LT for NELM warrant further investigation.

Liver transplantation and multivisceral transplantation in the management of patients with advanced neuroendocrine tumours

Orthotopic liver transplantation (OLT) represents a generally accepted albeit somewhat controversially discussed therapeutic strategy in highly selected patients with non-resectable hepatic metastases from neuroendocrine tumours (NET). Whilst there are some exclusion criteria, these are not universally followed, and the optimal set of inclusion parameters for deeming patients eligible has not yet been elucidated. This is due to heterogeneity in the study populations, as well differing approaches employed and also divergences in selection criteria between centres. Recent data have suggested that OLT may represent the most efficacious approach in terms of overall and disease-free survival to the management of NET metastatic to the liver when conducted in accordance with the modified Milan criteria. Therefore, a consensus set of selection criteria requires definition to facilitate stringent and fair allocation of deceased-donor organs, as well as consideration for living-donor organs. In the context of classically non-resectable metastatic tumour bulk, multivisceral transplantation with or without the liver may also be indicated, yet experience is very limited. In this review, we discuss the diagnostic work-up of patients in whom the aforementioned transplantation approaches are being considered, critically analyse the published experience and also anticipate future developments in this field, including a discussion of immediate and longer-term research priorities.

Liver transplantation for unresectable pancreatic neuroendocrine tumors with liver metastases in an era of transplant oncology

Patients with pancreatic neuroendocrine tumors (pNETs) very often present with a metastatic disease at the first diagnosis. Liver transplantation (LT) for unresectable pNET with liver metastases (pNETLM) has been described to prolong survival in highly selected patients, although outcomes were worse than those of patients who underwent LT for gastrointestinal NETLM (GI-NETLM). In this review, several proposed criteria are described with their rationale and controversies. Most of the data used to establish these criteria do not reflect the recent improvements of non-surgical treatments that has changed the landscape of treatment for pNETs, including the development of peptide receptor radionuclide therapy and molecular-targeted agents (sunitinib and everolimus). Properly designed studies are necessary to define the role of down-staging and bridging therapy prior to LT incorporating systemic chemotherapy using these molecular-targeted agents. Also, given the indolent nature of low or intermediate grade pNETs, the best endpoint to compare the efficacy of each treatment option for patients with pNETLM has yet to be determined. Lastly, the definition of "unresectable" remains ambiguous. The indication of the conventional technique of two-staged liver resection with portal vein embolization or the new technique of associating liver partition and portal vein ligation for staged hepatectomy to expand the resectability of wide-spread metastatic liver tumors has been controversial. In an era of transplant oncology, LT should be the last resort for patients who are considered unresectable and otherwise untreatable after an exhaustive multidisciplinary team discussion by all experts in the field. In conclusion, although its long-term outcomes have been promising, the role of LT for unresectable pNETLM as a curative or palliative treatment remains unclear. A well-designed randomized control study is required to elucidate the clinical impact of LT for pNETLM.

Con: Liver transplantation for expanded criteria malignant diseases

Organ shortage requires policies and guidelines to aid organ allocation along the principles of urgency or utility. Identifying patients with significant benefit and withholding liver transplantation (LT) from patients too sick for transplantation are ongoing challenges, in particular in patients with malignancies. An arbitrary threshold of >50% 5-year overall survival (OS) is broadly considered a minimum standard for LT. In patients transplanted for intrahepatic cholangiocarcinoma (iCC), this was only achieved in select cases and when the tumor had a diameter of <2 cm. In patients with extrahepatic and hilar cholangiocarcinoma (CCC), strict selection criteria and combined preoperative radiotherapy/chemotherapy according to the Mayo protocol showed that acceptable longterm results can be achieved in a single high-volume center but are difficult to repeat elsewhere. Furthermore, only rigorously selected patients with neuroendocrine tumors (NETs) meeting the NET Milan criteria adopted by United Network for Organ Sharing can also have >50% 5-year OS. A prospective study in patients with unresectable colorectal cancer metastases in the liver has shown promising OS rates, but further prospective trials are warranted. Current evidence shows that none of the proposed expanded malignant criteria justify deviation of scarce donor organs to patients with hilar CCC, iCC > 2 cm, metastatic NET beyond NET Milan criteria, or metastatic colorectal cancer (CRC) outside clinical trials. Liver Transplantation 24 104-111 2018 AASLD.

The place of liver transplantation in the treatment of hepatic metastases from neuroendocrine tumors: Pros and cons

Liver metastases occur in nearly half of NET patients (MNETs) and heavily affect prognosis, with 5-yr. OS around 19-38%. Although it is difficult to show outcome differences for available treatments, due to the long course of disease, surgery for MNETs remains the most effective option in terms of survival and symptom control. Since MNETs frequently present as an oligo-metastatic, liver-limited disease, unresectable in 80% of cases, liver transplantation (LT) has emerged as a potential curative treatment. Nevertheless, experience with LT for MNETs is limited and burdened by highly heterogeneous outcomes and significant recurrence rate, mostly explained by the variability of selection criteria. Several prognostic factors have been identified: extended surgery on primary tumor associated to LT, elderly patients, pancreatic primary (pNET), extensive liver involvement, poorly differentiated tumors, high Ki67 levels and short wait time to LT. A proper patients' selection based on these data (Milan NET criteria) allows a significant survival advantage over non-transplant strategies, with excellent outcomes in recent series (69-97.2% 5-yr. OS) as opposed to patients undergoing non-surgical treatments (34-50.9%). Evidence indicates LT as the best option for selected patients with MNETs. The use of organs for MNETs is therefore justified.

Donor-Derived Hepatic Neuroendocrine Tumor: Pause Before Proceeding With Liver Retransplantation

Gastrointestinal neuroendocrine tumors (NET) are rare but the age-adjusted incidence in the United States has increased, possibly due to improved radiographic and endoscopic detection. In advanced NET, hepatic metastases are common. Orthotopic liver transplant (OLT) is currently considered an acceptable therapy for selected patients with limited hepatic disease or liver metastases where complete resection is thought to have curative intent. The development of NET of donor origin is very uncommon after organ transplant, and it is unclear if the same treatment strategies applied to hepatic NET would also be efficacious after OLT. Here, we describe a unique case of an OLT recipient with a donor-derived NET that was treated with redo OLT as the primary therapy. The donor-derived NET recurred in the recipient's second liver allograft suggesting an extrahepatic reservoir. This case describes the natural history of such a rare event. Here, we highlight the treatment options for hepatic NET and challenge the role of OLT for a donor-derived hepatic NET.

Liver transplantation for hepatobiliary malignancies: a new era of "Transplant Oncology" has begun

The indications of liver transplantation for hepatobiliary malignancies have been carefully expanded in a stepwise fashion, despite the fundamental limitations in oncological, immunological, and technical aspects. A new era of "Transplant Oncology," the fusion of transplant surgery and surgical oncology, has begun, and we stand at the dawn of a paradigm shift in multidisciplinary cancer treatment. For hepatocellular carcinoma, new strategies have been undertaken to select recipients based on biological and dynamic markers instead of conventional morphological and static parameters, opening the doors for a more deliberate expansion of the Milan criteria and locoregional therapies before liver transplantation. Neoadjuvant chemoradiation therapy followed by liver transplantation for unresectable perihilar cholangiocarcinoma developed by the Mayo Clinic provided excellent outcomes in a US multicenter study; however, the surgical indications are not necessarily universal and await international validation. Similarly, an aggressive multidisciplinary approach has been applied for other tumors, including intrahepatic cholangiocarcinoma, hepatoblastoma, liver metastases from colorectal and neuroendocrine primary and gastrointestinal stromal tumors as well as rare tumors, such as hepatic undifferentiated embryonal sarcoma and infantile choriocarcinoma. In conclusion, liver transplantation is an important option for hepatobiliary malignancies; however, prospective studies are urgently needed to ensure the appropriate patient selection, organ allocation and living donation policies, and administration of antineoplastic immunosuppression.

The role of 90Y-radioembolization in downstaging primary and secondary hepatic malignancies: a systematic review

Radioembolization (RE) is an emerging treatment strategy for patients with primary hepatic malignancies and metastatic liver disease. Though RE is primarily performed in the palliative setting, a shift toward the curative setting is seen. Currently, hepatic resection and in selected cases liver transplantation are the only curative options for patients with a hepatic malignancy. Unfortunately, at diagnosis most patients are not eligible for liver surgery due to the imbalance between the necessary liver resection and the remaining liver remnant. However, in borderline resectable cases, tumor volume reduction and/or increasing the future liver remnant can lead to a resectable situation. The combination of selective tumor treatment, the induction of hypertrophy of untreated liver segments, and its favourable toxicity profile make RE an appealing strategy for downstaging. The present review discusses the possibilities for RE in the preoperative setting as a downstaging tool or as a bridge to liver transplantation.