CDK4 and melanoma: Other studies have provided evidence that some tumor suppressor genes, such as PTEN, p16 (inhibitor of CDK4/6), p14 (inhibitor of MDM2), RAS-association domain family 1 (RASSF1A) (cell cycle regulator), and O-6-Methyguanine-DNA Methyltransferase (MGMT) (a regulator of DNA repair) are silenced in melanoma cells through epigenetic mechanisms involving promoter hypermethylation [163].