MUTYH-associated tumor syndrome: The other face of MAP

MUTYH gene is involved in the base excision repair (BER) mechanism and its pathogenic alterations are associated with colorectal polyposis and cancer. MUTYH-associated polyposis (MAP) is a condition which is inherited in an autosomal recessive manner. MAP patients, beyond colorectal cancer (CRC), may develop other types of tumors, including duodenal, breast, ovarian, pancreatic, bladder and skin cancers. Carriers of biallelic MUTYH likely pathogenic/pathogenic variants exhibit a high lifetime risk of CRC, though cancer risk evidence becomes less clear when monoallelic carriers and extraintestinal tumors are considered. However, several studies recently reported an increased genetic susceptibility to cancer also for carriers of germline monoallelic MUTYH mutations. Moreover, experimental evidence highlighted the MUTYH involvement in many other biological functions. In future, MUTYH mutation carriers might benefit from new target therapies involving the use of PD-1 or KRAS inhibitors. Therefore, "MUTYH-associated tumor syndrome" might be the most appropriate term, due to the multiplicity of tumors observed in MAP patients and different biological contexts in which MUTYH acts as a "playmaker". In this Review, we will investigate the impact of germline mono- and biallelic MUTYH mutations on cancer risk, providing a proposal for clinical surveillance of mutation carriers.