When studying the molecular profiles of MSI tumors regardless of whether the tumor is Lynch syndrome-associated or sporadic, a number of oncogenic mutations can be found, including mutations in KRAS, NRAS, BRAF, PIK3CA, APC, TP53, etc. Specifically, KRAS is observed in MSI tumors with a frequency of 30–37% in endometrial, small bowel, and colorectal cancers, and at 15–28% in gastric cancer [29,86,96,116,117,118]. The gene discussed is KRAS; the disease is Lynch syndrome.