Tumors of more than one tissue type
- Malignant mesenchymoma.
- Malignant Triton tumor.
- Malignant ectomesenchymoma.
Tumors of unknown histogenesis
- Alveolar soft part sarcoma (ASPS).
- Clear cell sarcoma (malignant melanoma of soft parts [MMSP]).
- Desmoplastic small round cell tumor.
- Epithelioid sarcoma.
- Synovial sarcoma.
- Undifferentiated soft tissue sarcoma.
Tumors of vascular structures
Selected Soft Tissue Sarcomas in Children
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.[5,14] ASPS is considered a chemoresistant tumor. In children, ASPS often presents with metastases, and sometimes has a very indolent course. Pediatric ASPS seems to have a better outcome than its adult counterpart. In a series of 19 treated patients, one group reported a 5-year overall survival (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 and 53% at 10 years from diagnosis. Survival was better for smaller tumors (?5 cm) and completely resected tumors.[Level of evidence: 3iiA] 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 ASPS. There are sporadic reports of objective responses to interferon-alpha, bevacizumab, and sunitinib.[21,22,23]
Clear cell sarcoma
Clear cell sarcoma (malignant melanoma), also called clear cell sarcoma of tendons and aponeuroses, is somewhat similar to cutaneous malignant melanoma, but is cytogenetically distinct; most cases have a t(12;22)(q13;q12) translocation that has not been reported in melanoma. Patients who have small, localized tumors with low mitotic rate, and intermediate histologic grade fare best.
Dermatofibrosarcoma is a rare tumor, but many of the reported cases arise in children. The tumor has a consistent chromosomal translocation t(17;22)(q22;q13) that juxtaposes the COL1A1 gene with the PDGF-beta gene. Most tumors are cured by surgical resection. When surgical resection cannot be accomplished or the tumor is recurrent, treatment with imatinib has been effective.
Desmoid tumors are low-grade malignancies with very low potential to metastasize. The tumors are locally infiltrating, and surgical control can be difficult because of the need to preserve normal structures. These tumors also have a high potential for local recurrence. Desmoid tumors have a highly variable natural history, including well documented examples of spontaneous regression. Mutations in exon 3 of the beta-catenin gene are seen in over 80% of desmoid tumors and the mutation 45F has been associated with an increased risk of disease recurrence. Repeated surgical resection can sometimes bring recurrent lesions under control.