Evaluation of tumor and treatment response

All patients were preoperatively evaluated by physical examination, colonoscopy, abdominopelvic computed tomography (APCT), chest CT, pelvic MRI, and routine laboratory tests, including serum CEA measurements. The tumor location was defined as the distance from the anal verge (AV) to the lowest margin of the tumor on MRI or sigmoidoscopy. Treatment response to CRT was assessed using APCT, pelvic MRI, sigmoidoscopy, and routine laboratory tests at 4–5 wk after CRT. Surgery was performed 6–8 wk after CRT and included low anterior resection with colorectal or coloanal anastomosis, abdominoperineal resection, Hartmann’s operation, and total proctocolectomy. Pathologic results were reported according to the Seventh American Joint Committee on Cancer TNM staging system. Treatment response to CRT and tumor regression grade (TRG) were evaluated by experienced pathologists at the study center in accordance with the American Joint Committee on Cancer TRG system[13,14].