Monarch Disease Ontology identifier MONDO_0005864 (muscle cancer) is a malignant neoplasm affecting the skeletal or smooth muscles. Malignant neoplasms arising from the skeletal muscles are called rhabdomyosarcomas. Malignant neoplasms arising from the smooth muscles are called leiomyosarcomas. Also known as: cancer of muscle structure, malignant muscle neoplasm, malignant muscle structure neoplasm, malignant muscle tumor, malignant muscle tumour, malignant neoplasm of muscle, malignant neoplasm of muscle structure, malignant neoplasm of the muscle.