CDKN2A and cancer: For example, melanoma ranks among the top tumors for mutational burden and commonly does not express p16ink4a, but mutation of p53 is very uncommon in melanoma.10–12 On the other hand, cutaneous squamous cell carcinoma, one of the most common cancers in humans, more commonly has p53 mutation than loss of p16ink4a.13–15 Another observation is that while many tumors completely lack p16 expression, complete loss of p53 function is uncommon.