Phase II study of preoperative chemoradiation with S-1 plus oxaliplatin in patients with locally advanced rectal cancer.

A phase II study of preoperative chemoradiation (CRT) with S-1 plus oxaliplatin in patients with locally advanced rectal cancer was conducted. The total radiotherapy dose was 50.4 Gy. Chemotherapy consisted of oxaliplatin 50 mg/m(2) on days 1, 8, 22 and 29 and S-1 80 mg/m(2) per day on days 1-14 and 22-35. The tumor apparent diffusion coefficient (ADC) was measured using diffusion-weighted magnetic resonance imaging (DW-MRI) before and after CRT. Total mesorectal excision was performed within 6 ± 2 weeks. The primary end-point was the pathological complete response (pCR) rate. A total of 38 patients were enrolled. The pCR rate was 22.9% (8/35; 95% CI, 10.9-42.1), and 10 (28.6%) patients showed near-total tumor regression. There was no grade 4 adverse event, and grade 3 adverse events included leukopenia (5.4%), diarrhea (5.4%), anorexia (2.7%) and nausea (2.7%). The tumor ADC was calculated in 38 patients (including those who participated in the phase I study). The post-CRT ADC (P = 0.037) and the percentage change in ADC (P = 0.026) were significantly correlated with pathological response. In conclusion, preoperative CRT with S-1 plus oxaliplatin showed promising results in pathological responses and favorable toxicity profiles.