For instance, the promoter containing CpG islands of breast cancer cells was selectively hypermethylated to inactivation of tumor suppressor gene expression, such as cell cycle regulator (p16INK4a and p14ARF), apoptotic regulator (APC, HIC1, and TWIST), and DNA repair genes (GSTP1, BRCA1, and MGMT). This evidence concerns the gene CDKN2A and breast cancer.