Morelli and colleagues showed, by analyzing serial circulating tumor DNA (ctDNA) samples of 62 RAS WT mCRC patients whose tumors developed resistance to EGFR inhibition (EGFRi), that the KRAS and EGFR mutant allele fraction (MAF) was inversely correlated with the time since last administration of anti-EGFR MAbs [21]. This evidence concerns the gene EGFR and neoplasm.