Survival Impact of KRAS Mutation in Metastatic Colorectal Cancer (mccr) under First-Line Treatment.

3547 Background: Activating mutations in the MAPK pathway are predictive biomarkers in mCCR and 50% of patients (pts) present KRAS mutations. There is a large spectrum of molecular aberrations with a lack of data regarding tumor side correlations and their impact on treatment response and overall survival. Methods: Retrospective cohort of mCRC pts and KRAS activating mutations treated between 2019-2022 in a tertiary cancer center in Brazil. KRAS gene was analyzed by next-generation sequencing in tumor tissue samples. Electronic medical records were reviewed with case report forms registered in RedCap software. The primary endpoint was Overall survival (OS), estimated using Kaplan-Meir and compared with the log-rank test. Cox proportional models were applied to estimate hazard ratios (HR). Results: We included 490 patients with a mean age of 59 years (y), mostly male, 51.4%. Primary left-side location was present in 65.5% and liver metastasis in 66.7%. The spectrum of KRAS mutations found were G12D (31.2%), G12V (20.2%), G13D (15.1%), G12C (9.4%), G12A (4.9%), G12S (3.5%), and G12R (2%). First line regimen was 5-FU and Oxaliplatin (mFLOX) in 84.9% (n=388), with a median PFS of 9.2 months (95%CI 7.8 - 11.6) and OS of 21 months (95%CI;19-23) in this group. Treatment related outcomes in first-line therapy at first evaluation were 40% partial response, 20.4% stable disease, 30,9% disease progression and 1.3% complete response. G12S mutation was associated with better PFS 18.62 vs. 8.75m compared with other codon mutations (HR:0.52;95%CI 0.28-0.98) and OS NR vs. 21.58m HR (HR:0.48;95%CI;0.24-0.97). G12R was associated with worse PFS 5.31 vs. 9.90 m (HR:2.2;95%CI;1.09-4.47) and OS 17.89 vs. 21.88m (HR:1.61;0.79-3.24). Sideness was not associated with prolonged response or overall survival right-sided tumors 20.72 vs. vs. left-sided tumors 22.14m (HR:1.04;95%CI;0.82-1.31). Conclusions: Specific mutated codons in the KRAS gene impact PFS and OS independently of primary tumor sidedness. G12S mutation demonstrated an improved OS and PFS. [Table: see text]