CDKN2A and breast cancer: The literature data indicated that more than 100 genes have been hypermethylated in primary breast tumors and breast cancer cell lines, i.e., PTEN (Phosphatase And Tensin Homolog), RARB (Retinoic Acid Receptor Beta), APC (APC Regulator Of WNT Signaling Pathway), CDKN2A (P16; Cyclin Dependent Kinase Inhibitor 2A), CDH1 (Cadherin 1), DAPK1 (Death Associated Protein Kinase 1), GSTP1 (Glutathione S-Transferase Pi 1), RASSF1 (Ras Association Domain Family Member 1), TIMP3 (TIMP Metallopeptidase Inhibitor 3), and MGMT (O-6-Methylguanine-DNA Methyltransferase) [13,47].