rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a malignant soft tissue sarcoma that arises from skeletal muscle progenitors, or rhabdomyoblasts. It is the most common soft tissue sarcoma of childhood and adolescence, though it can occur at any age. RMS can arise anywhere in the body but commonly involves the head and neck, genitourinary tract, abdomen, and limbs.

There are four main histologic subtypes: embryonal (ERMS), alveolar (ARMS), pleomorphic, and spindle cell/sclerosing. ERMS is more common in children; ARMS is associated with characteristic chromosomal translocations creating PAX3-FOXO1 or PAX7-FOXO1 fusion genes. Pleomorphic RMS tends to occur in adults and has a different prognosis; spindle cell/sclerosing RMS is a newer recognized category.

Diagnosis involves imaging to assess local extent (usually MRI) and staging (often CT of the chest for metastasis), followed by biopsy with histology and immunohistochemistry (desmin, myogenin, and MyoD1). Molecular testing identifies PAX-FOXO1 fusions in ARMS. Staging and risk assessment use systems such as the Intergroup Rhabdomyosarcoma Study (IRS) groups, taking into account site, resectability, nodal involvement, and presence of metastasis to guide therapy.

Treatment is multimodal, combining surgery when feasible, radiation therapy for local control, and multiagent chemotherapy (commonly vincristine, actinomycin D, and cyclophosphamide, known as VAC). For high-risk or metastatic disease, intensified regimens and clinical trials may be used. The plan is tailored to histologic subtype, stage, risk group, and patient age.

Prognosis varies by subtype and stage. Localized embryonal RMS tends to have a relatively favorable prognosis, with higher long-term survival in modern series, while alveolar RMS and metastatic disease carry poorer outcomes. Advances continue through risk-adapted therapy and ongoing clinical trials.