A comprehensive survey of tumor mutation burden (TMB) using the AACR GENIE cbioportal database: Pathogenesis of NTRK and RET fusion (NTRK+/RET+) positive colorectal (CRC).

33 Background: Receptor tyrosine kinase fusion (RTK+) has been identified in colorectal carcinoma (CRC). Tumor agnostic treatment has been approved in NTRK fusion ( NTRK+) and RET fusion ( RET+) positive solid tumor. However, overall response rate (ORR) was the lowest among entrectinib-treated NTRK+ CRC (20%, 2/10) and selpercatinib treated RET+ CRC (20%, 2/10) among all NTRK+ and RET+ solid tumors respectively. Methods: We surveyed all 58 human RTKs to identify RTK fusions in CRC and RET and NTRK fusions in other solid tumors using AACR GENIE cbioportal public version 13.0. We abstracted and compared the tumor mutation burden (TMB) of these fusions from the cbioportal database. Patient and tumor characteristics were also abstracted. Results: Among the 14812 unique CRC patients identified in the AACR GENIE cbioportal, a total of 153 unique RTK fusions were identified (44 with known fusion partners, 109 with intragenic rearrangement) in 27 out of the total 58 human RTKs. The most common RTK fusions in CRC were in FGFR1 (N = 23), EGFR (N = 21), ERBB2, NTRK1, RET, FGFR2 (N = 10 each), FLT1 and FLT3 (N = 9 each), FLT4 and ALK (N = 7 each). Considering only samples with identified fusion partners, the mean TMB was 66.6 +/-15.8 (mt/MB) for NTRK+ CRC (N = 9), and 35 +/-11.5 for RET+ CRC (N = 4), which were significantly higher when compared to mean number of 6.2 +/- 5.4 of TMB for all other RTK+ CRC (ALK, EGFR, FGFR1/2, ERBB4, FLT1/3/4, LMKT2, MET, NTRK2, PDGFR-b, ROS1) (N = 30, P< 0.05). Furthermore, NTRK+ CRC harbored significantly higher TMB than RET+ CRC (P = 0.003). The mean TMB was 4.0 +/- 1.9 for RET+ NSCLC (N = 65), 2.6 +/- 1.6 for RET+ Thyroid cancer (N = 52), which were both significantly lower than RET+ CRC. Mean TMB was 3.1 +/- 1.7 for NTRK+ glioma (N = 21), 3.3 +/- 1.7 for NTRK+ thyroid cancer (N = 21), 6.5+/-5.1 for NTRK+ Melanoma (N = 8), 5.9 +/- 3.4 for NTRK+ NSCLC (N = 7), 5.1 +/- 1.2 for NTRK+ breast cancer (N = 7) all of them were significantly lower than the mean TMB of NTRK+ CRC. 1482 (10.0%) patients with CRC had their MSI status reported. 3 out of 3 NTRK+ CRC patients with known MSI status were all MSI-H (100%). 12 out of 12 non-NTRK/non-RET RTK+ CRC patients were MSI-S. Conclusions: In this comprehensive survey of human RTK fusions in CRC, NRTK+ and RET+ CRC harbor significantly higher TMB compared to other RTK+ CRC or to other NTRK+/RET+ solid tumors. Limited data showed NTRK+ CRC were all MSI-H. NTRK+ and RET+ CRC are distinct molecular subtypes of CRC with unique pathogenesis from all other NTRK+ or RET+ solid tumors. We hypothesize that NTRK+/RET+ CRC may benefit from pembrolizumab that has been approved for histologic agnostic high TMB tumors rather than RET or NTRK tyrosine kinase inhibitors (low ORR in CRC) that also have histological agnostic indications.