We report 2 cases of carcinoma arising in anal fistula. Case 1: A 62-year-old man undergoing surgery for anal fistula underwent Seton's drainage 4 times to resolve recurrent disease 17 years after primary surgery. He developed a painful perianal tumor with mucinous discharge. A biopsy specimen showed well-differentiated adenocarcinoma. We conducted abdominoperineal resection (APR) and left inguinal lymph node dissection. Case 2: A 49-year-old man with chronic anal fistula and perianal abscess 18 years after primary surgery developed anal stenosis with large bowel obstruction. He underwent sigmoidstomy to relieve bowel obstruction. Biopsy of the anal fistula tract showed mucinous adenocarcinoma, necessitating APR. Despite postoperative chemoradiotherapy, local recurrence developed 5 years postoperatively. He died 6 years and 7 months after APR due to peritoneal carcinomatosis. Active biopsy of anal fistula and routine imaging may detect cancer early enough to improve survival.
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