CDKN2A and melanoma: Recently, exon sequencing approaches revealed additional mutations in individual members of the MAP3K and MAP2K families including MEK1 and MEK2. The AKT/mTOR pathway might be additionally activated mainly by loss-of-function mutations or deletions of the inhibiting phosphatase PTEN. Furthermore, typical impairment of senescence due to mutations, deletions or methylation of p16INK4/CDKN2A occurs in 30 to 70% of melanomas.