Evaluation of the prognostic impact of pathologic tumor regression grade on patients with colorectal cancer after preoperative chemoradiotherapy

Abstract Background The prognostic value of the pathological response to preoperative chemoradiotherapy (CRT) in rectal cancer (RC) remains unknown. Objectives We aimed to assess the predictive value of the response to CRT that was derived from an evaluation of the histological findings (whole‐section vs. representative‐section sampling) and attempted to determine an objective cut‐off value for the tumor regression grade (TRG). Methods We examined the association of the TRG with the outcomes (recurrence‐free survival [RFS] and overall survival [OS]) of 78 patients with RC. Patients with RC treated with preoperative CRT were divided into development (30 cases) and validation (48 cases) cohorts. The TRG was classified as grades I (Ia, Ib), II, and III. The cut‐off value was determined by receiver operating characteristic (ROC) curve analysis. Results The TRG determined from whole‐section sampling versus representative‐section sampling was more strongly correlated with patient survival. We found that in both cohorts, patients with a cut‐off value of <73% had a poor prognosis. Finally, the cut‐off value was found to be an independent predictive factor in both univariate and multivariate analysis. Conclusions The TRG that was used to evaluate patients with RC who underwent preoperative CRT was an independent prognostic factor for outcome.