Survival in metastatic microsatellite-stable colorectal cancer correlated with tumor mutation burden and mutations identified by next-generation sequencing

Background: Next-generation sequencing (NGS) identifies mutations and molecular abnormalities within tumors, including tumor mutation burden (TMB). If a solid tumor has high TMB, immune checkpoint inhibitors (ICIs) are approved as an option for treatment. Studies have been inconclusive regarding how effective ICI are in treating patients with colorectal cancer (CRC), and it is unclear if high TMB is a good prognostic marker for CRC. We collected data from NGS of CRC and correlated survival to both TMB and mutations of interest, as well as investigated the efficacy of ICI. Methods: This was a retrospective cohort analysis at a single institution, collecting NGS data from January 2018 to December 2020 in patients with CRC who were microsatellite-stable (MSS), n=161. Demographics, clinical data, and results from NGS were collected, and a survival analysis looking at TMB and selected mutations of interest was performed. Patients who were treated with ICI were assessed in a descriptive subset analysis. Results: Patients with CRC who were MSS and had high TMB trended towards worse survival [hazard ratio (HR) =1.38] though the result was not significant (P=0.28). Survival was significantly worse in patients with a KRAS mutation (HR =1.71, P=0.04) and/or a CDKN2A mutation (HR =4.45, P<0.001). In this study population, 12 patients with high TMB had treatment with ICI, with nine of these patients having shorter progression-free survival (PFS) between 0.7 and 4.1 months, and three patients having longer PFS of 26.3, 24.7, and 13.2 months. Conclusions: High TMB in MSS CRC did not show statistical difference in outcome. Mutations in KRAS and/or CDKN2A correlated with worse prognosis. Some patients with MSS CRC and high TMB responded to ICI, though there is a need to identify a better biomarker to predict which patients will have a good response to ICI therapy.