Proliferative Myositis

**Semantic type:** Neoplastic Process

**Definition:** A rapidly growing, poorly circumscribed, mass-forming proliferation that arises from the skeletal muscle. It is characterized by the presence of spindle-shaped fibroblasts, round ganglion-like cells, myxoid to collagenous stroma formation, and high mitotic activity. It recurs only rarely following local excision and does not metastasize.