A 64-year-old woman with a history of cervical intraepithelial neoplasia presents with a firm 3-cm mass protruding at the anal verge. Anoscopy shows a fixed mass just distal to the dentate line. A biopsy of the lesion is performed, which has the findings shown in the Figure. Colonoscopy findings are unremarkable and computed tomography of the chest, abdomen, and pelvis reveals no evidence of distant disease. Magnetic resonance imaging reveals no locoregional nodal or sphincter involvement. The next best step in management for this patient is: