Cyclooxygenase 2 expression in rectal cancer is of prognostic significance in patients receiving preoperative radiotherapy.

Abstract

To determine the effect of cyclooxygenase (COX)-2 expression on clinical behavior in irradiated and nonirradiated rectal carcinomas. Tumor samples were collected from 1,231 patients of the Dutch TME trial, in which rectal cancer patients were treated with standardized surgery and randomized for preoperative short-term (5 x 5 Gy) radiotherapy or no preoperative radiotherapy. Tissue microarrays were constructed from primary tumor material, and COX-2 expression was assessed by immunohistochemistry. Tumor cell apoptosis was determined by M30 immunostaining. A high level of COX-2 expression after radiotherapy was associated with low levels of tumor cell apoptosis (P=0.001). COX-2 expression had no significant effect on patient survival or tumor recurrence in nonirradiated tumors. However, in patients receiving preoperative radiotherapy, high level of COX-2 expression was associated with higher incidence of distant recurrences [P=0.003; hazard ratio (HR), 1.7; 95% confidence interval (95% CI), 1.2-2.5] and shorter disease-free survival (P=0.002; HR, 1.8; 95% CI, 1.2-2.5) and overall survival (P=0.009; HR, 1.5; 95% CI, 1.1-2.0), independent of patient age, tumor stage, tumor location, or the presence of tumor cells in the circumferential resection margin. A high level of COX-2 expression after preoperative radiotherapy in resection specimens is associated with apoptosis resistance, high distant recurrence rates, and a poor prognosis in rectal cancer.