[Diagnosis and Treatment of MSI-H Cancer in Gynecological Cancer].

Among gynecological cancers, microsatellite instability(MSI)is most commonly found in endometrial carcinoma. When an allelic variation is observed in multiple microsatellite regions, it is called MSI-high(MSI-H). Hereditary MSI-H endometrial cancer develops through a germline mutation ofthe mismatch repair(MMR)gene, resulting in Lynch syndrome, and increased risk ofsporadic MSI-H endometrial cancer is caused by somatic lineage mutations or methylation abnormalities. Clinical characteristics ofendometrial cancer involved in Lynch syndrome include symptoms such as onset at a younger age, a lower corpus segment at the site, earlier stage cancer, and varied histology, when compared with those ofthe sporadic cancer. Alternatively, somatic mutations ofthe MMR gene are highly heterogeneous; however, a meta-analysis showed no difference in prognosis between with and without MSI-H. MSI-H is considered to be a biomarker, showing the therapeutic effects of an immune checkpoint inhibitor. A recent randomized controlled trial(RCT)demonstrated that an immune checkpoint inhibitor was effective against colorectal cancer with MSI-H. An additional RCT proved its effectiveness for MSI-H solid cancers, regardless oforgan type, including endometrial cancer. As the number ofcases ofendometrial cancer is increasing in Japan, MSI-H may hold utility as a biomarker for new molecular-target drugs, including immune checkpoint inhibitors. Ongoing surveillance ofcarcinomas in patients and family members is important because endometrial carcinoma associated with Lynch syndrome is a hereditary tumor. However, there is currently no established surveillance method for endometrial cancer. To improve the overall prognosis ofpatients with Lynch syndrome, genetic counseling and cross-division management are necessary, and also establishing the system is urgently required.