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Rhabdomyosarcoma is a malignant soft tissue tumor which develops from cells of striated muscle. It is the most common form of tumor found in children and adolescents.
The annual incidence is 1/170,000. In children younger than 15 years, the annual incidence is estimated at 1/244,000.
The median age of diagnosis is 5 years. Rhabdomyosarcoma can develop anywhere in the body, including in sites where striated muscle does not normally occur. The most frequent locations are: the head and neck (40%), including tumors of the orbit and para-meningeal tumors, the genitourinary tract (20%) including tumors in the bladder and/or prostate, in the uterus and vagina, para-testicular tumors, and tumors in the limbs (20%) and trunk (10%). Rhabdomyosarcoma has a high risk of local relapse, a high risk of local extension to lymph nodes and a lower risk of metastases. There are two main histological subtypes of rhabdomyosarcoma: embryonic (80% of cases) and alveolar (15-20% of cases). Clinically there is little difference between the two types. The alveolar form occurs more readily in the limbs, nearly never in the orbits and more frequently affects the lymph nodes.
The cause of rhabdomyosarcoma is unknown, but a translocation t(2;13) is very often associated with the alveolar type.
Diagnosis is based on positive muscular markers and immunohistochemistry. The evidence of a translocation t(2;13) leads to diagnosis of alveolar forms.
Differential diagnoses include small round cell tumors (lymphoma, neuroblastoma, Ewing sarcoma; see these terms). It is possible to distinguish between tumors using immunohistochemistry. Some rhabdomyosarcomas are associated with a genetic predisposition to cancer as part of Li-Fraumeni syndrome or neurofibromatosis type 1 (see these terms).
Management and treatment
Treatment should be managed by a multidisciplinary team, expert in the treatment of childhood cancers. Initial surgery should only be considered if it can be completed, and completed without significant consequences. Chemotherapy is indicated in all other cases from diagnosis. Local treatment is carried out by secondary surgery, often complemented by radiotherapy. Alveolar forms require more intensive treatment than embryonic forms. The objective of current protocols is to avoid radiotherapy, if possible, in order to reduce long term sequelae.
Survival depends on the location of the tumor. In localized forms the survival rate is greater than 80% for tumors of the orbit, bladder, vagina and paratesticular region. The survival rate is in the order of 60-70% for other localized tumors. For patients with metastases at diagnosis the survival rate is lower, and adolescents and patients with osteo-medullar metastases have a survival rate of less than 20%.
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