CDK4 and melanoma: Recent studies of mucosal melanoma analyzed by next-generation sequencing demonstrated that mucosal melanomas have high chromosomal instability and often show structural variants of CDK4, MDM2, TERT, cyclin D1 (CCND1), and NOTCH2, leading to their amplification, along with losses of cyclin-dependent kinase inhibitor (CDKN) 2A/B, phosphatase and tensin homolog (PTEN) and p53 [10,11,17].