Preoperative chemoradiation with S-1 plus oxaliplatin in patients with locally advanced rectal cancer: Results of a phase II study and the role of apparent diffusion coefficient (ADC) by diffusion-weighted magnetic resonance imaging (DW MRI) for prediction of pathologic responses.

Abstract

629 Background: We conducted a phase II study of preoperative chemoradiation (CRT) with S-1, a novel oral fluoropyrimidine, plus oxaliplatin in patients (pts) with locally advanced rectal cancer. Tumor ADCs were measured by DW-MRI and were evaluated as a predictive marker for pathologic responses. Methods: Radiotherapy was delivered to a total 50.4 Gy. The recommended doses were determined by a previous phase I study; oxaliplatin 50 mg/m2/week on D1, 8, 22 and 29, and S-1 80 mg/m2/day on D1-14 and D22-35. Total mesorectal excision was performed within 6 ± 2 weeks. Primary endpoint was pathologic complete response (pCR) rate. The value of tumor ADCs by DW-MRI was measured before and after CRT, and was correlated with pathologic responses after surgery. Results: A total of 38 patients were enrolled; 22 (57.9%) were men and the median age was 54 years (range, 28-67). Of 35 patients who underwent curative surgery, 28 patients underwent sphincter-saving operations. There was no grade 4 toxicity, and grade 3 toxicities included leukopenia (2.7%), neutropenia (2.7%), anorexia (2.7%), nausea (2.7%) and diarrhea (8.8%). The pCR rate was 25.7% (8/35, 95% CI [10.9-42.1]) and additional 10 patients (28.6%) showed near total regressions of tumor. Tumor ADCs by DW-MRI were calculated in 38 patients (including phase I part). The post-CRT ADC and the ADC changes (ΔADC) were significantly correlated with pCR rate (post-CRT ADC: 1.52±0.46 vs. 1.07±0.58, p=0.037, ΔADC: 44.5% vs. -7.6%, p=0.026). Conclusions: Preoperative CRT with S-1 plus oxaliplatin showed promising results in pathologic responses and favorable toxicities profiles. Tumor ADC by DW-MRI seems to be a useful method for predicting responses. No significant financial relationships to disclose.