TP53 and neoplasm: A p53 (−) condition in immunohistochemical staining is associated with the wild-type p53 gene; however, some p53 (−) tumours with poor response to CRT may be associated with a complete loss of p53 protein due to a p53-null mutation, an acceleration of protein degradation (Hollstein et al, 1991), or the existence of another molecule that regulates radiation sensitivity in the p53 signalling pathway.