TP53 and head and neck cancer: Although we have not assessed if p53 is mutated in our cell lines, the data show an interesting pattern previously demonstrated by the group of Manuel Serrano in head and neck cancers, in which high levels of p21 do not correlate to p53 levels but does correlate with better survival rates [51], and in our case, more sensitize tumor cells to radiation (UM-HMC3A and 3B).