Ten cases (30%) harbored pathogenic somatic mutations affecting an MMR gene, including MLH1, MSH2, MSH6 or PMS2. Whole-exome sequencing-based MSI analysis revealed that 79% (26 of 33) of endometrial/ovarian cancers were MSI-H, whereas seven endometrial cancers (21%) were MSS. The gene discussed is MSH2; the disease is endometrial cancer.