MLH1 and hereditary nonpolyposis colon cancer: HNPCC patients with endometrial cancers have an inherited germline mutation in MLH-1, MSH-2, MSH-6, or PMS-2, but endometrial cancer only develops after the instauration of a deletion or mutation in the contralateral MLH-1, MSH-2, MSH-6, or PMS-2 allele.