Ntrk Gene Fusions In Biliary Tract Cancers

574 Background: Gene fusions involving one of the 3 neurotrophic tyrosine receptor kinases ( NTRK) have been identified in approximately 1% of solid tumors and inhibitors of TRK (e.g. larotrectinib) have been shown to have anti-tumor activity regardless of tumor type. NTRK gene fusions have been previously reported in bilio-pancreatic cancers. It is of interest therefore to determine the incidence and molecular characteristics of NTRK gene fusions in patients with bilio-pancreatic cancers. Methods: Formalin-fixed paraffin-embedded archival blocks from surgical resections, biopsies or cytological samples of biliary tract tumors including intra-hepatic cholangiocarcinoma (IH), extra-hepatic cholangiocarcinoma (EH), perihilar cholangiocarcinoma (PH) and gallbladder tumors (G) were selected/retrieved from the tumor bank of the CUB Hôpital Erasme between January 2010 and July 2019. A two-step diagnostic method incorporating immunohistochemistry (IHC) screening followed by NGS analysis was used. Pan–TRK IHC (monoclonal antibody clone EPR17341 [AbCam, Cambridge, MA]) was used for the screening method. Staining intensity (negative, weak, moderate or strong) and localization (cytoplasmic or nuclear) were evaluated. The presence of at least weak staining tumor cells led to testing by a RNA-based NGS panel (Oncomine Focus Assay, ThermoFisher scientific). Results: 145 archival tumors samples (81 surgical resections, 48 biopsies and 16 cytology) have been selected, including 61 IH, 32 PH, 26 EH and 26 G (67 female and 78 male). 134 samples were suitable to perform IHC. 17 samples were IHC positive. Intensity of staining was weak in 16 samples and moderate in one. Staining location was cytoplasmic (14/17), nuclear (2/17), and nuclear+cytoplasmic (1/17). NGS testing of the 17 IHC positive samples revealed a single NTRK3 gene fusion ( ETV6(4)- NTRK3(14)). In this case (female patient with a poorly differentiated PH, deceased), IHC had a weak focal cytoplasmic and nuclear staining. Overall in the patients screened by IHC and confirmed by NGS, the percentage of NTRK fusions was 0.75%. Conclusions: NTRK gene fusions are rare in biliary cancers but testing is of high interest due to the emergence of possible treatment with specific TRK inhibitors.