575P - Biopsy Specimens Obtained 7 Days After Starting Chemoradiotherapy (CRT) Provides Reliable Predictors of Response to CRT for Rectal Cancer

Abstract

ABSTRACT Background Preoperative CRT is a standard treatment for locally advanced rectal cancer (LARC). The histologic response to CRT or the downstaging has been reported to be closely related to oncologic outcomes. Various biomarkers in biopsy specimens obtained before CRT have been investigated as predictors of response, however, reliable predictive biomarkers remain to be established. Methods The study group comprised 101 consecutive patients with LARC who received preoperative CRT of 45Gy with oral uracil/tegafur (UFT) or S-1. We evaluated histologic findings on H-E staining and immunohistochemical expressions of Ki67, p53, p21, and apoptosis in biopsy specimens obtained before CRT and 7 days after starting CRT. These findings were contrasted with the rate of histologic marked regression and the degree of tumor shrinkage. Results In biopsy specimens obtained before CRT, the degree of tumor shrinkage on barium enema (BE) were significantly greater in patients with p21-positive tumors (52 ± 11%) than in those with p21-negative tumors (45 ± 16%) (p Conclusions Immunohistochemical expressions of p21 and apoptosis together with histologic changes on H-E-stained biopsy specimens obtained 7 days after starting CRT are strong predictors of response to CRT. Disclosure All authors have declared no conflicts of interest.