Treatment of Newly Diagnosed Childhood Soft Tissue Sarcoma
Tumors of Uncertain Differentiation
Tumors of uncertain differentiation include the following tumor subtypes:
- Alveolar soft part sarcoma.
- Clear cell sarcoma of soft tissue.
- Desmoplastic small round cell tumor.
- Epithelioid sarcoma.
- Extrarenal rhabdoid tumor.
- Extraskeletal myxoid chondrosarcoma.
- Primitive neuroectodermal tumor (PNET)/extraskeletal Ewing tumor.
- Synovial sarcoma.
- Undifferentiated sarcoma; sarcoma, not otherwise specified (NOS).
Alveolar soft part sarcoma
This is a tumor of uncertain histogenesis. A consistent chromosomal translocation t(X;17)(p11.2;q25) juxtaposes the ASPSCR1 gene with the TFE3 gene.[70,71] In children, alveolar soft part sarcoma often presents with metastases  and sometimes has a very indolent course. A subset of renal tumors found in young people was previously considered to be renal cell carcinoma, but the subset now appears to be genetically related to alveolar soft part sarcoma.
Pediatric alveolar soft part sarcoma seems to have a better outcome than its adult counterpart. In a series of 19 treated patients, one group reported a 5-year OS rate of 80%, a 91% OS rate for patients with localized disease, a 100% OS rate for patients with tumors 5 cm or smaller, and a 31% OS rate for patients with tumors larger than 5 cm. In another series of 33 patients, OS was 68% at 5 years from diagnosis and 53% at 10 years from diagnosis. Survival was better for smaller tumors (≤5 cm) and completely resected tumors.[Level of evidence: 3iiA]
The standard approach is complete resection of the primary lesion. If complete excision is not feasible, radiation therapy should be administered.
The value of adjuvant chemotherapy in completely resected alveolar soft part sarcoma remains unproven, particularly because patients with unresected or metastatic tumors failed to respond to chemotherapeutic agents frequently used to treat STSs. Alveolar soft part sarcoma is considered a chemoresistant tumor. There are sporadic reports of objective responses to interferon-alpha, bevacizumab, and sunitinib.[79,80,81,82]
Patients with alveolar soft part sarcoma may relapse several years after a prolonged period of apparent remission. Because these tumors are rare, all children with alveolar soft part sarcoma should be considered for prospective clinical trials.