NRAS and colorectal carcinoma: Currently, studies have shown that inherent genetic mechanisms including KRAS/NRAS/BRAF mutations and ERBB2, MET amplification are the main reasons for the resistance of CRC patients to anti-EGFR therapy, but there are still 30% of cases that do not respond to anti-EGFR therapy from an unknown, apparently non-genetic resistance mechanism [6–8, 11–13].