Evaluation of Combined Modality Protons and Hepatic Transplantation for Hilar Cholangiocarcinoma

Liver and bile duct resection with lymphadenectomy is the standard of care for patients with hilar cholangiocarcinoma. Unfortunately, resection is only possible in a minority of patients for many reasons including, the extent of cancer or the presence of background primary sclerosing cholangitis (PSC). For patients with a background of PSC, liver transplantation is a potential treatment, and it was recently approved as an indication for a commissioned pilot service evaluation of liver transplantation in the UK.

Until recently, the use of liver transplantation for hilar cholangiocarcinoma was confined to a few centres in the United States. The initial publications from the Mayo Clinic and Nebraska, as well as more recent experience from other centres, support strict selection protocols to identify patients likely to benefit from liver transplantation. In 2000, the initial experience at the Mayo Clinic in which 19 patients enrolled in a pre-transplant neoadjuvant therapy protocol was published. 11 patients underwent subsequent liver transplantation. Of the 8 with long term follow up (median 44 months), only one patient developed cancer recurrence. Similarly, the long-term experience of patients in Nebraska, where 11 patients underwent liver transplantation after neoadjuvant chemoradiotherapy was published in 2002. 5 of the 11 patients were alive and disease free at a median follow up of 7.5 years .

Most recent experience is based on adopting the Mayo protocol. In general, the inclusion criteria define patients with early cancers, with a dominant stricture or tumour less than 3cm. Intra and extrahepatic disease including any site of nodal metastases precluded selection. Controversially, histology or cytology was not considered essential for diagnosis of cholangiocarcinoma by most centres. Elevated Ca 19.9 of >100, Fluorescence In Situ Hybridization (FISH) polysomy 9p21 or tumour mass in the presence of a dominant stricture were considered sufficient for enrolment. Prior (attempts at) trans-peritoneal biopsy was another exclusion criterion based on concerns of increased risk of tumour dissemination. Neoadjuvant therapy involved external beam radiation therapy (EBRT) with concurrent chemotherapy (chemo sensitisation), followed by brachytherapy whenever possible. Patients were then re-staged and remain on systemic chemotherapy until the time of transplant.

A recent review looked at all studies from 2000 until 2019. 20 studies with 428 patients were eligible for analysis. The pooled 1, 3-, and 5-year overall survival rates following liver transplantation without neoadjuvant therapy (n=156) were 71.2%. In patients who had neoadjuvant therapy prior to transplantation (n=272), the survival improved to 82.8% at 1,3 and 5 years respectively.

The cancer recurrence rate was 51.7% in patients who did not receive neoadjuvant therapy compared to 24.1% for patients who had. Only 4 of the 20 studies reported pre-transplant histological confirmation of adenocarcinoma or malignant/suspicious cells on cytology. 98% of liver explants from studies not using neoadjuvant therapy confirmed malignancy, compared to 50.5% in those who had received neoadjuvant therapy. Patients in whom malignancy was not found are presumed to have had complete pathological response to neoadjuvant therapy (approximately 50% following neoadjuvant therapy). Patients with background PSC had better outcomes compared to patients with de novo cancers.

Study Design \& development of an evaluative commissioning study within ECIP:

It is not possible to design EMPHATIC, a study for patients with unresectable cholangiocarcinoma, as a randomised controlled trial (RCT), because there is no ethically acceptable control arm. In an RCT, patients in a theoretical control arm would be offered either no transplant, or no neoadjuvant therapy prior to the transplant. Based on the published literature summarised above, the adverse anticipated outcomes of patients in such a control arm would not be considered justified.

Neoadjuvant therapy is required to control the tumour prior to transplant. In the Mayo protocol described above, patients received external beam (chemo)radiotherapy followed by brachytherapy, and thereafter received chemotherapy until the time of transplant. Unfortunately, in the UK, brachytherapy services were not seen as a viable option, and hence the Mayo protocol is not feasible.

There is good scientific rationale that proton beam radiotherapy (PBT) offers the optimal technique for delivering neoadjuvant therapy as it is non-invasive, and spares as much functional liver as possible, compared with alternatives such as photon-EBRT techniques or invasive techniques (e.g. brachytherapy). Compared with photon-EBRT techniques, PBT delivers highly conformal radiotherapy, with a significantly reduced integral body dose, and no exit beam. It is expected to be associated with an improved toxicity profile.