Perianal mucinous adenocarcinoma: unusual case presentations and review of the literature.

Perianal mucinous adenocarcinoma is a rare cancer constituting 3 to 11 per cent of all anal carcinomas. It may arise de novo or from a fistula or abscess cavity. We present two cases of this disease process. Case One is a 52-year-old man with a chronic history of perianal abscesses who presented to the emergency room with a large bowel obstruction. He required diversion and wide local excision with lateral internal sphincterotomy for relief of the obstruction. Pathology from the excised material revealed the unexpected diagnosis of invasive mucinous adenocarcinoma of the anus. Case Two is a 59-year-old man with a chronic history of complex fistulas and abscesses who presented to our office with a horseshoe fistula and deep postanal space abscess. Because of the nonhealing nature of the wound, biopsies from the abscess crater, fistulous tract, and the perianal skin opening were taken. The pathology department identified the specimens as invasive mucinous adenocarcinoma of the anal canal. This is an aggressive cancer often misdiagnosed clinically as benign pathology. A high index of suspicion and biopsy of fistulous tracts and abscesses are the keys to early diagnosis and treatment. With combination chemotherapy and radiation therapy in conjunction with aggressive surgical resection long-term survival might be obtained.