Hereditary nonpolyposis colon cancer associated cancers arise from MLH1 and MSH2 germline mutations and rarely involve mutations of other genes (Liu et al, 1996; Peltomaki and Vasen, 1997) or MLH1 promoter region methylation (Wheeler et al, 2000; Potocnik et al, 2001; Yamamoto et al, 2002). The gene discussed is MSH2; the disease is hereditary nonpolyposis colon cancer.