KRAS mutation and microsatellite instability in colorectal cancer: Screening pattern and mutational landscape across the US.

Abstract

e15138 Background: To assess screening patterns for KRAS mutation and microsatellite instability (MSI), associated mutational prevalence in colorectal cancer (CRC), and whether mutational screening affects survival. Methods: Patients with adenocarcinoma of the colon, sigmoid, and rectum were included from the 2010-2015 National Cancer Database. Socioeconomic, geographic and cancer factors were correlated with screening patterns. Propensity score matching was used to account for confounding. Overall survival was assessed in the matched cohort via Cox proportional hazards models. Results: 371,669 patients were included, of which 113,197 (30.4%) were screened: n=63,967 for MSI, n=33,319 for KRAS, and n=15,911 for MSI + KRAS. Younger patients with private insurance, high income locally advanced and metastatic sigmoid CRC treated at academic centers in Middle Atlantic and New England states were more likely to be screened. MSI was more prevalent among older female Caucasians from East South Central and Middle Atlantic States. KRAS mutation showed no significant discrepancies according to patient age or US geography, but was more prevalent among female African Americans. KRAS mutation was associated with locally advanced and metastatic CRC. MSI was more common in localized, non-metastatic CRC. Distinct mutational patterns were evident among primary CRC sites, with highest mutation rates in cecum/appendix and ascending colon (table). In the propensity score matched cohort with balanced distribution of confounders (n=157,678), mutational screening was not associated with overall survival (HR=1.012, 95% CI: 0.99-1.03, p=0.15). MSI versus MSS did not significantly influence patients´ overall survival (matched cohort n=26,014, HR=1.00, 95% CI: 0.96-1.05, p=0.88). Kras mutation versus wildtype showed decreased overall survival after accounting for confounders (matched cohort n=28,084, HR=1.11, 95% CI: 1.07-1.15, p<0.001). Conclusions: Testing for MSI and Kras mutation in CRC shows distinct patterns across the US, but does not influence outcomes. Decreased overall survival is observed in those patients with Kras mutation versus wildtype. [Table: see text]