EGFR and colorectal carcinoma: ctDNA genomic features of progression on prior cetuximab or panitumumab include the presence of subclonal RAS mutation (VAF < 50% of the maximum VAF in the sample), multiple concurrent RAS mutations, and/or EGFR mutations.29 In a previously validated large cohort of patients with metastatic CRC with and without anti-EGFR exposure, the presence of any one of these variables was highly predictive of prior anti-EGFR exposure (positive predictive value, 98.3%; specificity, 98.7%).29