Anal mucinous adenocarcinoma arising in long standing fistula-in-ano

Perianal mucinous adenocarcinoma is an unusual but well described malignancy constituting approximately 3 to 11% of all anal carcinoma. The pathology is thought to develop from one of three types, the distal part of the rectum, the mucin-secreting columnar epithelium of the anal glands, and from chronic fistula-in-ano. The association of carcinoma with anal fistula may manifest itself in several ways: a fistula may be associated with cancer elsewhere in the colon cancer may present as a fistula or cancer may develop in anal fistula. Mucinous adenocarcinoma of the anus supervening on a long-standing chronic anal fistula is an extremely rare disease with less then 150 cases reported in the literature, mainly single patient reports. The key to long term survival seems to be a high index of suspicion in those patients with long-standing perianal fistula. Chemotherapy in combination with external beam radiation followed by abdomino-perineal resection seems to be the most appropriate therapy.