Smooth muscle neoplasms of the rectum and anal canal.

Forty-eight patients who presented to St. Mark's Hospital, London between 1948 and 1979 with smooth muscle neoplasms of the rectum or anal canal have been reviewed. Twenty-six tumours arose from the muscularis mucosae of the rectum. These lesions were small, asymptomatic and did not recur after local removal. Eighteen tumours arose from the muscularis externa of the rectum. Local excision of these resulted in a high local recurrence rate regardless of the degree of differentiation of the tumour but long-term survival figures were similar whether the tumours were treated by local or radical techniques. However, the prognosis did relate to the degree of tumour differentiation, being worst in the poorly differentiated group. In four cases the smooth muscle tumour arose from the internal sphincter of the anal canal.