[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 longstanding perianal fistula. Chemotherapy in combination with external beam radiation followed by abdomino-perineal resection seems to be the most appropriate therapy.