A 67-year-old man recently underwent a colonoscopy with resection of a 1.2-cm pedunculated colon polyp from the sigmoid colon. The area from which the polyp was completely removed was marked with ink. Pathology showed well-differentiated adenocarcinoma invading into the submucosa of the stalk, with a 2-mm margin. No lymphovascular invasion was noted. What is the optimal management for this lesion?