KRAS and neoplasm: Analyses of tumor samples from the PRIME study in mCRC have shown that more comprehensive RAS testing (i.e., exon 2, 3, and 4 of both KRAS and NRAS) better selects those patients more likely to respond to EGFR inhibitors, with RAS WT populations experiencing a statistically significant improvement in OS versus chemotherapy alone (26 versus 20.2 months; p = 0.04) [14].