Treatment Trends and Clinical Outcomes of Left-Sided RAS/RAF Wild-Type Metastatic Colorectal Cancer in the United States

Background: Post hoc analysis of the CALGB/SWOG 80405 trial suggests that anti-EGFR therapy may be superior to bevacizumab when added to first-line chemotherapy in patients with metastatic colorectal cancer (mCRC) who have left-sided primary tumors. We evaluated trends in use of anti-EGFR agents in patients with left-sided RAS/RAF wild-type (WT) mCRC and compared clinical outcomes among the most commonly used treatment strategies. Methods: A nationwide electronic health record (EHR)-derived deidentified database was reviewed for patients with left-sided RAS/RAF WT mCRC. Treatment trends over time were assessed by fitting a linear model to the percentage of patients receiving anti-EGFR therapy. A propensity score weighted Cox model was used to compare overall survival (OS) stratified by first-line targeted therapy received. Results: A total of 1,607 patients with left-sided RAS/RAF WT mCRC received standard first line chemotherapy. Of these, 965 (60%) received bevacizumab and 186 (12%) received an anti-EGFR agent. The percentage of patients receiving an anti-EGFR increased from 9% in 2013 to 16% in 2018. Median OS for patients treated with chemotherapy alone was 27.3 months (95% CI, 24.8-32.3), 27.5 months with bevacizumab (95% CI, 25.8-28.9; hazard ratio [HR], 0.88; P=.33), and 42.9 months with an anti-EGFR agent (95% CI, 36.0 to not reached; HR, 0.52; P=.005). Conclusions: This analysis suggests that chemotherapy with bevacizumab remained the most widely used first-line treatment strategy for patients with left-sided RAS/RAF WT mCRC in the United States in 2018. Despite this preference, treatment with an anti-EGFR agent was associated with improved OS.