Skeletal muscle tumors.

Subdivided into embryonal, alveolar, and pleomorphic subtypes.

Most common soft tissue sarcoma in children and adolescents.

Suspected to derive from primitive mesenchymal cells committed to developing into striated muscles.

Accounts for more than half of soft tissue sarcomas and children.

Incidence of 4.5 cases per million children and adolescents per year.

Accounts for 5% of childhood cancers and between 2-5% of adult soft tissue sarcomas.

Arise from striated muscle progenitor cells.

Can arrise at any site.

In children-70% long-term survival rate, thirty percent relapse and 50%-95% of these patients die.

Cure rate for children with localized disease is 70%.

Pediatric patients that present with metastases have a 5-year progression free survival of less than 30%.

Around 40% of all cases occur in adults.

In children-14-20% of children who die from rhabdomyosarcoma have brain metastases, but only 2% have evidence of brain involvement during the course of their illness.

There are two main histological types: embryonal subtype, which accounts for approximately 80% of all pediatric rhabdomyosarcomas, and the more aggressive alveolar subtype which comprises 15-20% of cases and is characterized by a chromosomal translocation involving the fusion of the transcription factor genes FOXO1 and either PAC3 or PAX7.

Embryonal subtype is the most common in childhood.

Embryonal type ranges from primitive mesenchymal appearing cells to highly differentiated muscle cells.

Alveolar tumors more common among adolescents, often arising in the extremities and carry a worse prognosis.

Alveolar subtype consists of round cells with high nuclear to chromatin ratios forming glandular like or alveolar spaces.

Alveolar soft part sarcoma is a rare soft tissue sarcoma that carries a sprecific t(X;17)(p11;q25), involving alveolar soft tissue sarcoma-transcription factor E 3 fusion.

Alveolar soft part sarcoma behaves indolently couples with a paradoxical high metastatic rate.

Alveolar soft part sarcoma responds to anti-angiogenic agents like pazopanib, with response rates 35-60%.

Pleomorhic lesions are composed of rhabdomyoblasts which most commonly present on the lower extremities.

In adults, 5-10 year survival approximately 30%.

Five-survival rates for patients with tumors less than 5 cm, 5 to 10 cm and more than 10 cm approximately 60%, 14% and 0%, respectively.

In adults-patients with localized/locoregional disease at presentation have a 44% 5-year survival rate and there are no survivors among patients presenting with metastatic disease.

In adults-age, nodal and histologic subtype do not appear to be associated with survival.

Childhood types predilection in the head and genitourinary regions and prognosis correlated to histologic subtype.

Adult type predominately in the extremities and largely not responsive to chemotherapy and is associated with a poor prognosis irrespective of histologic type.

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