An aggressive malignant smooth muscle neoplasm that arises from the colon. It is characterized by a proliferation of neoplastic spindle cells. The disease is colon leiomyosarcoma (MONDO_0003351, a Monarch Disease Ontology entry). Also known as: colonic leiomyosarcoma, leiomyosarcoma of colon, leiomyosarcoma of the colon.