CDKN1A and head and neck squamous cell carcinoma: This prompted us to examine expression of p53 and reporters of p53 function (MDM2, p53, Phospho-p53 [Ser15], TIGAR and p21 [CDKN1A]) in the HPV-positive SCCHN cell lines, with the hypothesis that there may be residual wild-type p53 function sufficient to prevent metabolic re-programming.