NTRK fusion positive colorectal cancer as a unique subset of CRC with high tumor mutation burden and microsatellite instability.

Abstract

3544 Background: Neurotrophin receptor tyrosine kinase ( NTRK) gene fusions are rare but actionable oncogenic drivers that are present in a wide variety of solid tumors. This study aims to identify the frequency and the clinicopathologic and genetic features of NTRK-driven colorectal cancers (CRC). Methods: Colonic and rectal tumor DNA specimen from colorectal cancer patients submitted for molecular profiling at a CLIA-certified genomics laboratory in China that performed NTRK1/2/3 fusion detection by hybridization-based targeted next generation sequencing (NGS) were retrospectively reviewed. Patients’ demographic, clinical characteristics, and treatment history were retrieved from the database for further evaluation. Results: A total of 2,519 unique Chinese colorectal cancer cases were profiled from April 2016 to May 2020, and 17 NTRK+ fusion events were identified (0.7%, 17/2,519) consisting of 14 cases of NTRK1+ and 3 cases of NTRK3+ fusions. Furthermore, thirteen out of 17 NTRK+ CRC tumors (76%) were microsatellite instability-high (MSI-H) tumors, a much higher rate than that of the molecularly unselected CRC population (8%) or NTRK+ non-CRC tumors ( < 1%). NTRK+ CRC patients also had increased tumor mutation burden (median TMB = 65 mut/MB) compared to that of non- NTRK+ CRC (median TMB = 7.7 mut/MB) or NTRK+ non-CRC tumors (median TMB = 4 mut/MB). POLE/POLD1 mutations were also enriched in NTRK+ CRC (8/17, 47%) relative to molecularly unstratified CRC patients (8%) with over half carrying concurrent POLE and POLD1 mutations. TPM3 was the most common fusion partner of NTRK1 (78%, N = 14), followed by LMNA and TRP. Three NTRK3+ CRC were identified (ETV6-NTRK3, RUNX1-NTRK3, CSNK1G1-NTRK3). RNF43 (71%) was the most frequently mutated gene and the aberrations of RNF43 and ARID1 were significantly enriched in MSI-positive NTRK+ tumors as compared to the MSS NTRK+ subgroup. TP53 (53%) and APC (35%) aberrations frequently co-occurred with NTRK fusions, whereas the majority of the NTRK+ cohort were RAS/BRAF wildtype, except in one case that an oncogenic KRAS Q61R variant co-occurred with RUNX1-NTRK3. Conclusions: NTRK+ colorectal cancer is rare. In addition to the absence of canonical driver mutations, NTRK+ tumors demonstrated increased tumor mutation burden, higher frequency of microsatellite instability, and an enrichment of POLE/POLD1 mutations relative to molecularly unselected CRC population.