Primary leiomyosarcoma of the colon.

Primary leiomyosarcomas of the gastrointestinal (GI) tract are extremely rare and highly aggressive neoplasms, and only a small number of true cases have been reported since the concept of GI stromal tumors was established. Here, we report a case of a primary leiomyosarcoma of the transverse colon. A 46-year-old Japanese male with a large mass in the right upper abdomen was admitted to our hospital.