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e16664 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 have been shown to have anti-tumor activity regardless of tumor type. NTRK gene fusions have been previously reported in bilio-pancreatic tumors. It is of interest therefore to determine incidence and molecular characteristics of NTRK gene fusions in these patients. Methods: Formalin-fixed paraffin-embedded archival blocks from surgical resections, biopsies or cytological samples of biliary tract tumors (BTC) including intra-hepatic (IH), extra-hepatic (EH), perihilar cholangiocarcinoma (PH) and gallbladder tumors (G), and pancreatic adenocarcinoma (PA) were retrieved from the tumor bank of CUB Hôpital Erasme between JAN 2010 and OCT 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) pattern (diffuse, focal or rare positive cells), 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: For BTC, 162 archival tumors samples have been selected. 149 samples were suitable to perform IHC.17 samples were IHC positive including 9 IH, 3 PH, 2 EH and 3 G tumor samples. 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). Pattern of staining was rare positive cells (2/17), focal (4/17) and diffuse (11/17). NGS testing of the 17 IHC positive samples revealed a single NTRK3 gene fusion ( ETV6(4)- NTRK3(14)). In this PH tumor, IHC had a weak focal cytoplasmic and nuclear staining. Overall in the patients screened by IHC and confirmed by NGS, percentage of NTRK fusions was 0.67 %. For PA, 319 archival tumor samples have been selected and 297 were suitable for IHC. 19 samples were IHC positive. Intensity of staining was weak in 18 samples and moderate in one. Staining location was cytoplasmic (18/19) and nuclear (1/19). Pattern of staining was focal in 2 cases and diffuse in 17 cases. No fusion was detected by NGS. Conclusions: NTRK gene fusions are rare in bilio-pancreatic cancers but testing is of high interest due to the emergence of possible treatment with specific TRK inhibitors. These results support the use of NGS to confirm positive IHC results during diagnostic screening.

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.