Purpose: RAS and BRAF mutations can be detected as a mechanism of acquired resistance in circulating tumor (ct) DNA in patients with metastatic colorectal cancer treated with anti-epidermal growth factor receptor therapy.
Methods: RAS and BRAF mutational status was assessed in ctDNA in a baseline plasma sample and a serum sample collected at the time of the last available determination (named secondary extraction) from patients with KRAS exon 2 wild-type metastatic colorectal cancer treated in two first-line prospective biomarker-designed clinical trials (PULSE, ClinicalTrials.gov identifier: NCT01288339; and POSIBA, ClincialTrials.gov identifier: NCT01276379).
Results: Analysis of extended RAS and BRAF in tissue and plasma from 178 patients with KRAS exon 2 wild-type metastatic colorectal cancer showed a sensitivity of 64.1% and a specificity of 90%. The median overall survival (OS) of baseline patients with RAS and BRAF mutations in ctDNA was 22.3 months (95% CI, 15.6 to 29 months) and 8.9 months (95% CI, 6.3 to 11.4 months), respectively, which was significantly inferior to the median OS of 40.4 months (95% CI, 35.9 to 44.9 months) in two patients with wild-type disease (P < .001). Acquisition of RAS/BRAF mutations occurred in nine of 63 patients (14%) with progressive disease (PD; ie, blood draw within 1 month before PD or after PD) compared with six of 73 patients (8%) with no PD or blood extraction for ctDNA analysis before 1 month of PD (P = .47). Median OS in patients with RAS/BRAF acquisition was 23.9 months (95% CI, 19.7 to 27.9 months) compared with 40.6 months (95% CI, not reached to not reached) in patients who remained free of mutations (P = .016).
Conclusion: Our results confirm that baseline RAS and BRAF testing in ctDNA discriminates survival. The emergence of RAS/BRAF mutations has limited relevance for the time to progression to anti-epidermal growth factor receptor therapy.