diAGNOSIS: Mismatch Repair Deficient Gastric CancerMismatch repair cancer syndrome (MMRCS) is a cancer syndrome associated with biallelic DNA mismatch repair mutations.[1] It is also known as Turcot syndrome (after Jacques Turcot, who described the condition in 1959) and by several other names.[1]In MMRCS, neoplasia typically occurs in both the gut and the central nervous system (CNS).[1] In the large intestine, multiple colonic polyps develop; in the CNS, brain tumors.