A rapidly growing malignant mesenchymal neoplasm. It is characterized by the presence of round cells with myoblastic differentiation and a fibrovascular stroma resembling an alveolar growth pattern. The tumor usually presents in the extremities.

A soft tissue tumor that is most common in older children and teenagers. It begins in embryonic muscle cells (cells that develop into muscles in the body). It can occur at many places in the body, but usually occurs in the trunk, arms, or legs.

(rhabdomyosarcoma, alveolar) A form of RHABDOMYOSARCOMA occurring mainly in adolescents and young adults, affecting muscles of the extremities, trunk, orbital region, etc. It is extremely malignant, metastasizing widely at an early stage. Few cures have been achieved and the prognosis is poor. Alveolar refers to its microscopic appearance simulating the cells of the respiratory alveolus. (Holland et al., Cancer Medicine, 3d ed, p2188)