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. This evidence concerns the gene MLH1 and endometrial cancer.