CDKN2A, also known as cyclin-dependent kinase Inhibitor 2A, is a gene on chromosome 9. The gene codes for two proteins, both acting as tumor suppressors.
Somatic mutations of CDKN2A are common in the majority of human cancers, with estimates that CDKN2a is the second most commonly inactivated gene in cancerous tissues after p53. Germline mutations of CDKN2A are associated with familial melanoma, glioblastoma and pancreatic cancer.Wikipedia
The degree to which risk for melanoma is increased due to a CDKN2A mutation considered pathogenic is unclear. As stated in [PMID 20831418], published penetrance estimates through age 80 for CDKN2A mutations range as high as 67% [PMID 12072543]. Researchers in the GEM Study estimated the risk for melanoma among CDKN2A mutation carriers to be 28% through age 80 [PMID 16234564]. The authors of the previously cited paper ultimately settled on telling participants in their study that CDKN2A mutations conferred an overall 30–65% risk for melanoma by age 80 and could also increase the risk of a new primary melanoma.
In a 2017 study, family members of CDKN2A mutation carriers were found to also be at higher risk for melanoma, even though they (the family members) had non-mutated CDKN2A genes. Known as phenocopying, this phenomena is presumably caused by other risk-modifying genes or exposure patterns that increase the probability of the specific phenotype - in this case, melanoma - developing.[PMID 29215650]