Furthermore, although early studies by Ohnishi et al(10) and Tanaka et al(11) demonstrated that the xanthine oxidase inhibitor, ACA, was a chemopreventive agent that suppressed tumor formation in the oral cavity and colon of rats, subsequent studies revealed that ACA exerted positive anti-tumorigenic effects on leukemia and breast and multiple myeloma cancers (12–14). This evidence concerns the gene XDH and neoplasm.