p53 expression in human rectal tissue after radiotherapy: upregulation in normal mucosa versus functional loss in rectal carcinomas

Purpose: In vitro, ionizing radiation of epithelial cells leads to upregulation of wild-type p53 and subsequent induction of p21 waf1. The effect of radiotherapy (RT) on the expression of these proteins in patients is unknown. We assessed the influence of RT on the expression of p53 and p21 waf1 in normal mucosa and rectal carcinomas in vivo. Methods: Tumor and normal tissue samples were derived from rectal cancer patients randomized in a clinical trial in which the value of preoperative RT was evaluated. p53 and p21 waf1 expression was determined in 51 irradiated and 52 nonirradiated patients using immunohistochemistry. Results: In normal mucosa, both p53 and p21 waf1 were strongly upregulated after RT compared with the expression in unirradiated normal tissue ( p