Patients with endometrial carcinoma in the HNPCC population have an inherited germline mutation in MLH1, MSH2, MSH6, or PMS2 (first hit) but endometrial carcinoma develops only after the initiation of a deletion or mutation in the contralateral MLH1, MSH2, MSH6, or PMS2 allele (second hit) in endometrial cells [7, 8]. The gene discussed is MSH2; the disease is endometrial carcinoma.