Preoperatively Irradiated Rectal Carcinoma: Analysis of the Histopathologic Response and Predictive Value of Proliferating Cell Nuclear Antigen Immunostaining

Abstract

Objectives: To investigate the relationship between the histopathologic effects of preoperative chemoradiotherapy in rectal cancer and the proteins, proliferating cell nuclear antigen (PCNA) and p53. Methods: Samples from 73 tumors were examined. The histopathologic effects observed in the resected specimens induced by preoperative chemoradiotherapy were correlated with the inmunohistochemical expression of PCNA and p53 in biopsies obtained by rectoscopy before chemoradiotherapy. Results: Thirty-five tumors showed a high PCNA index (48%). Nuclear accumulation of p53 protein was detected in 53 tumors (72%). Specimens were assigned one of four grades based on the amount of residual viable tumor. Three neoplasms (4%) showed complete regression; 8 other carcinomas (11%) showed only small numbers of tumor cells scattered within the field of stromal reaction. In these cases, it was considered that the tumor had responded significantly to radiotherapy. Tumors with a high PCNA index responded to chemoradiotherapy more frequently (8/35; 72%) than tumors with a low index (3/38; 43%) (p = 0.07). p53-negative tumors responded more frequently (4/20; 20%) than positive tumors (7/53; 13.2%) (p = 0.50). When pathologic and immunohistochemical characteristics of the tumors were included in a logistic regression model, only high PCNA index (odds ratio 5.35, 95% confidence interval 1.07–26.7) (p = 0.04) was significantly associated with the histologic response to preoperative chemoradiotherapy. Conclusion: High proliferative activity of rectal cancer, as determined by PCNA immunostaining, is predictive of the response to preoperative chemoradiotherapy.