We report the case of a 45-year-old man, who at the age of 24 had total proctocolectomy with ileal W-pouch anal anastomosis for familial adenomatous polyposis. A follow-up transanal endoscopy performed at the age of 38 revealed approximately 30 polyps in the ileal pouch, which were then confirmed by biopsy to be tubular adenomas. A transanal endoscopy performed at the age of 44 revealed an 8 mm 0-Is lesion located approximately 1 cm proximal to the ileal pouch-anal anastomosis, which was then removed by EMR. Histopathological analysis showed the presence of well-differentiated tubular adenocarcinoma in adenoma. To date, no recurrence of adenocarcinoma has been confirmed in follow-up transanal endoscopies. We have experienced treating a case of adenocarcinoma arising in the ileal pouch through the adenoma-carcinoma sequence after total proctocolectomy with ileal pouch-anal anastomosis for familial adenomatous polyposis. For early diagnosis and prompt treatment, it is important to perform periodic surveillance of the ileal pouch and conduct aggressive endoscopic resection when a large adenoma exceeding 10 mm is found.
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