We noticed that compared to control, in DMBA-treated animals levels of Cdk4 (Fig. 5a) and Ccnd1 (Fig. 5b) were increased respectively an average ~3.0- and 1.0-fold in adjacent mammary tissues; and an additional ~6.0- and 12.0-fold increase was seen, respectively, for Cdk4 and Ccnd1, in mammary tumors. This evidence concerns the gene CDK4 and breast cancer.