A 62-year-old woman has a sigmoid colectomy for colon cancer seen at colonoscopy. Final pathology reveals a T3N0M0 lesion (0/22 lymph nodes postive, widely negative margins). Her 1-year surveillance colonoscopy is normal with a well-healed colorectal anastomosis. Eighteen months postcolectomy the patient reports weight loss; her carcinoembryonic antigen (CEA) level is noted to be 12.4. The most likely site of recurrent disease is