Relationship between histologic response and the degree of tumor shrinkage after chemoradiotherapy in patients with locally advanced rectal cancer.

ABSTRACT

BACKGROUND: Preoperative chemoradiotherapy (CRT) significantly decreases local recurrence in advanced rectal cancer. We studied whether the degree of tumor shrinkage can be used as a predictor of histologic response. METHODS: The subjects were 114 patients with locally advanced rectal cancer who underwent total mesorectal excision after receiving radiotherapy combined with uracil/tegafur (UFT) or S-1. The degree of tumor shrinkage based on barium enema examination and magnetic resonance imaging (MRI) were assessed before CRT and immediately before surgery. RESULTS: A histologic complete response (ypCR), histologic marked regression, T and N downstaging were associated with significantly higher tumor-shrinkage rates on barium enema (P < 0.01, P < 0.01, P < 0.01, and P < 0.01, respectively) as well as on MRI (P < 0.01, P < 0.01, P < 0.01, and P = 0.01, respectively). On multivariate analysis, ypCR and histologic marked regression were significantly related only to tumor-shrinkage rates on barium enema (P < 0.01 and P < 0.01, respectively), and were not related to tumor-shrinkage rates on MRI. CONCLUSIONS: The degree of tumor shrinkage is closely related to the final histologic response. Two-dimensionally evaluated tumor-shrinkage rates based on barium enema are adequate for the prediction of histologic response.