Prediction of histologic regression on the basis of colonoscopic findings in patients with locally advanced middle and lower rectal cancer who receive preoperative chemoradiotherapy.

Objective: Preoperative chemoradiotherapy significantly reduces local recurrence in patients with locally advanced rectal cancer (LARC). Various biomarkers have been proposed as predictors of the response to chemoradiotherapy, but their reliability remains uncertain.

Methods: Surgery in combination with preoperative radiation and UFT- or S-1-based chemotherapy was used to treat 102 patients with LARC. Colonoscopy was performed before the start of chemoradiotherapy and immediately before surgery. Patients in whom the tumor mound flattened remarkably or disappeared were evaluated as responders. The endoscopic response was compared with histologic regression and the degree of tumor shrinkage.

Results: Histologic regression was marked in 59.8% of patients according to the Tumor Regression Grade criteria and 44.1% according to the Japanese Classification of Colorectal Carcinoma criteria. The degree of tumor shrinkage was 34.3% on average. Marked histologic regression was present in a significantly higher proportion of responders than non-responders (p = 0.01). The degree of tumor shrinkage was significantly greater in responders (38.8%) than in non-responders (30.9%; p < 0.01). T-downstaging was significantly more common among responders (64.3%) than non-responders (26.7%; p = 0.04).

Conclusions: Morphologic changes on colonoscopy were associated with the degree of tumor shrinkage, histologic regression, and T-downstaging, suggesting that such findings can be used to predict the response to preoperative chemoradiotherapy.