Rhabdomyosarcoma (RMS) is a highly aggressive form of cancer that develops from mesenchymal cells that have failed to fully differentiate into myocytes of skeletal muscle. Cells of the tumor are identified as rhabdomyoblasts. The four subtypes are embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma, pleomorphic rhabdomyosarcoma, and spindle-cell/sclerosing rhabdomyosarcoma. Embryonal and alveolar are the main groups, and these types are the most common soft tissue sarcomas of childhood and adolescence. The pleomorphic type is usually found in adults. It is generally considered to be a disease of childhood, as the vast majority of cases occur in those below the age of 18. It is commonly described as one of the small-blue-round-cell tumors of childhood due to its appearance on an H&E stain. Despite being relatively rare, it accounts for approximately 40% of all recorded soft-tissue sarcomas. RMS can occur in any soft-tissue site in the body, but is primarily found in the head, neck, orbit, genitourinary tract, genitals, and extremities. No clear risk factors have been identified, but the disease has been associated with some congenital abnormalities. Signs and symptoms vary according to tumor site, and prognosis is closely tied to the location of the primary tumor. Common sites of metastasis include the lungs, bone marrow, and bones. There are many classification systems for RMS and a variety of defined histological types. Embryonal rhabdomyosarcoma is the most common type and comprises about 60% of cases. Outcomes vary considerably, with five-year survival rates between 35 and 95%, depending on the type of RMS involved, so clear diagnosis is critical for effective treatment and management. Treatment usually involves a combination of surgery, chemotherapy, and radiation. 60 to 70% of newly diagnosed patients with nonmetastatic disease can be cured using this combined approach to therapy. Despite aggressive multimodality treatment, less than 20% of patients with metastatic RMS are able to be cured of their disease.

Reference
Wiki: Rhabdomyosarcoma