Population-based Screening for BRAF V600E in Metastatic Colorectal Cancer Reveals Increased Prevalence and Poor Prognosis

mutations portend poor prognosis in metastatic colorectal cancer (mCRC); however, the true prevalence and prognosis are unknown, as unwell patients may not undergo sequencing. We reviewed a population-based cohort of 1,898 patients with colorectal cancer that underwent reflexive IHC mismatch repair (MMR) and testing. Outcomes among IHC-detected mCRC ( ) were compared with patients with next-generation sequencing (NGS)-identified -mutated mCRC from two institutions ( ) with patients spanning from 2004 to 2018. All-stage population prevalence of was 12.5% (238/1,898) and did not differ between early and metastatic stages ( = 0.094). Prevalence among mCRC was 10.6% (61/575), of whom 51 (83.6%) were referred to oncology and 26 (42.6%) had NGS testing. had worse median overall survival (mOS) than [5.5 vs. 20.4 months; HR, 2.90; 95% confidence interval (CI), 1.89-4.45; < 0.0001], which persisted in multivariate analysis ( < 0.0001). Across a combined NGS and IHC cohort, tumors with deficient MMR showed worse mOS compared with MMR proficient tumors (8.9 vs. 17.2 months; HR, 1.46; 95% CI, 0.96-2.27; = 0.043). In this combined cohort, first-line progression-free survival was 5.9 months, with minimal differences between regimens. Within the population-based cohort, attrition between treatment lines was high with only 60.7% receiving first-line chemotherapy and 26.2% receiving second line. Patients with -mutated mCRC have a worse prognosis than previously suggested, potentially arising from referral bias for testing. High attrition between lines of therapy suggests efficacious therapies need to be prioritized early for patients to benefit.