A 56-year-old man presents to the office with biopsy-proven midrectal adenocarcinoma on colonoscopy. Rigid sigmoidoscopy in the office shows a 5-cm circumferential mass 8 cm from the anal verge. Staging evaluation with computed tomography of the chest, abdomen, and pelvis and magnetic resonance imaging of the pelvis preoperatively demonstrates a T3N1M0 cancer. What is the next step in management for this patient?