CDKN1A and melanoma: For example, the RB1 pathway is a primary driver of skin cancers, with mutations in RB1, CDKN2A/p16, CDKN1A/p21, CDKN1B/p27, CDKN2B/p15, CCNE1/cyclin E, and CCND1/cyclin D, collectively, in 26.4% of melanomas (Hayward et al, 2017).