Leiomyosarcoma of the colon and rectum.

Leiomyosarcoma of the colon is an uncommon lesion and may appear throughout the colon. Early diagnosis is seldom accomplished before complications such as bleeding or obstruction appear. Sometimes it is histologically difficult to distinguish between a benign and a mlaignant leiomyoma. Some leiomyomas have biologic evidence of malignancy. Five cases of leiomyosarcoma are described, one of which was histologically diagnosed as a leiomyoma, but two years later, at laparotomy, metastases were found.