MONDO_0017386 (pleomorphic rhabdomyosarcoma) is an aggressive malignant mesenchymal neoplasm with skeletal muscle differentiation, occurring in adults and rarely in children. The tumor is characterized by the presence of bizarre round, spindle, and polygonal cells. Clinical presentation includes a rapidly enlarging painful mass usually of the lower extremities. Also known as: anaplastic rhabdomyosarcoma, pleomorphic rhabdomyosarcoma, adult type.