[A case of minimal-sized adenocarcinoma in a fistula-in-ano].

The patient was 47 year-old man with a simple intermuscular fistula-in-ano. Fistulectomy revealed that there was a small mucinous adenocarcinoma. The tumor was small and localized in the wall of the fistula and the muscular invasion was not recognized. The mucin contained a little O-acylated sainomucin, and the origin of the tumor was considered as anal gland cell. This case appears as one evidence that the cancer in fistula-in-ano originates from the anal gland cell in the fistula.