Neoplastic transformation in longstanding fistula-in-ano.

A case in which an infiltrating mucinous carcinoma developed within a suprasphincteric fistula-in-ano is presented. The diagnosis was suspected on biopsy and confirmed by repeat biopsy. The clinical and histological features of this case establish with certainty that the carcinoma arose within the fistula and was not a secondary manifestation of the tumour. It is suggested that this rare complication of chronic fistula-in-ano may be prevented by prompt expert management of complex primary fistula.