Prognostic effect of RAS/BRAF mutations in patients (pts) with metastatic colorectal cancer (mCRC).

191 Background: Somatic alterations in KRAS and BRAF have prognostic as well as predictive impact in pts with mCRC; however, the differential impact of various somatic alterations in these genes need further characterization. We analyzed the prognostic impact of specific somatic mutations in K RAS and BRAF in mCRC pts. Methods: We retrospectively reviewed the electronic medical records of pts with mCRC at our institution who underwent comprehensive genomic profiling (CGP) utilizing the Foundation One assay. Prevalence of genetic alterations was estimated using proportions and compared between groups using a chi-squared test. Patients were followed for survival from metastatic diagnosis until death or last follow-up, with left truncation at the time of CGP. Kaplan-Meier estimates were used to estimate overall survival, and groups were compared using a Cox-regression based likelihood ratio test. Results: 192 pts were identified - median age at diagnosis was 55 years, 62% (119/192) presented with metachronous metastatic disease, and 28% (54/192) had a rectal primary. Somatic mutations in KRAS were found in 49% (95/192) pts, and 53% (50/95) had a left sided primary (p = 0.3). Majority of the KRAS mutations localized to codon 12 (72/95 -76%), KRAS G12C comprised 12% (11/95). Median Overall Survival (mOS) of KRAS mutated pts was 3.0 years compared to 3.5 years for KRAS wild type (WT) pts (p = 0.5). Median OS of pts with different KRAS mutations were as follows: codon 12 mutations (excluding G12C) - 2.7 years; KRAS G12C – 5.2 years; non-codon 12 KRAS mutations - 4.8 years. BRAF mutations were identified in 7.8% (15/192) pts, and 67% (10/15) had a right sided primary (p = 0.062). BRAF V600E represented the most common alteration in BRAF – 87% (13/15). Patients with BRAF mutation had a mOS of 1.8 years compared to 3.1 years for BRAF WT pts (p = 0.2). Median OS of pts with different BRAF mutations were as follows: BRAF V600E – 1.8 years and BRAF non V600E - 2.1 years (p = 0.4). Conclusions: The numerically higher mOS in pts with KRAS G12C and non-codon 12 KRAS mutations merit further biologic characterization with functional assays. Individualized therapeutic strategies must be conceptualized for mCRC pts with specific RAS/BRAF mutations, considering their widely disparate prognosis and putative downstream signaling mechanisms. Dynamic molecular simulation to understand conformational changes in proteins associated with specific mutations will be pivotal to optimizing precision therapeutic strategies.