CDKN2A and head and neck squamous cell carcinoma: Analyses of 279 cases of SCCHN by The Cancer Genome Atlas identified p53 mutations in 84% of HPV-negative tumours and only in 3% of HPV-positive tumours, supporting the thesis that smoking and alcohol related cases of SCCHN are associated with near-universal loss of p53 function through its mutation and with CDKN2A inactivation.