Promoter DNA of the CDO1 gene has been reported to be frequently methylated in various cancers, including breast [6–9], esophagus [11], lung [8, 18, 19], bladder [8], gastric [8], colorectal [8, 20], biliary tract [13], hepatocyte [21], renal clear-cell cancer [10], and testicular germ cell cancers [22]. The gene discussed is CDO1; the disease is cancer.