Cellular and Histopathologic Classification
Desmoplastic small round cell tumor
Desmoplastic small round cell tumor is a primitive sarcoma that most frequently involves the abdomen, pelvis, or tissues around the testes.[31,32,33] The tumor occurs mainly in males and invades locally but may spread to the lungs and elsewhere. Cytogenetic studies of these tumors have demonstrated the recurrent translocation t(11;22)(p13;q12), which has been characterized as a fusion of the WT1 and EWS genes.
Epithelioid sarcoma is a rare mesenchymal tumor of uncertain histogenesis which displays multilineage differentiation. It is characterized by inactivation of the SMARC/INI1 gene which is present in both conventional and proximal types of epithelioid sarcoma. There are also alterations in rhabdoid tumors, but the mechanisms of inactivation seem to be distinctive. This tumor commonly presents as a slow growing firm nodule based in the deep soft tissue; the proximal type predominantly affects adults and involves the axial skeleton and proximal sites. The tumor is highly aggressive and has a propensity for lymph node metastases. The proximal type has a more aggressive clinical behavior. In a review of 30 pediatric patients with epithelioid sarcoma, the median age at presentation was 12 years, responses to chemotherapy were reported in 40% of patients using sarcoma-based regimens, and 60% of patients were alive at 5 years following initial diagnosis.
Inflammatory myofibroblastic tumor
Inflammatory myofibroblastic tumor (IMT) is an incompletely characterized neoplasm of intermediate biologic potential. It recurs frequently but metastasizes rarely. Roughly half of IMTs exhibit a clonal mutation that activates the anaplastic lymphoma kinase (ALK)-receptor tyrosine kinase gene at chromosome 2p23. There are no well-documented responses to chemotherapy. A case report described a partial response in a patient with recurrent IMT who was treated with crizotinib, an ATP-competitive inhibitor of the ALK and MET tyrosine kinases. There are case reports of response to either steroids or nonsteroidal anti-inflammatory drugs.
A 24-year retrospective analysis of the Italian cooperative group identified one child with leiomyosarcoma. A retrospective analysis of the St. Jude Children's Research Hospital experience from 1962 to 1996 identified 40 children with NRSTS; none had leiomyosarcoma. Among 43 children with HIV/AIDS who developed tumors, eight developed Epstein-Barr virus-associated leiomyosarcoma. Survivors of hereditary retinoblastoma have a statistically significant increased risk of developing leiomyosarcoma and 78% of these were diagnosed 30 years and older after the initial diagnosis of retinoblastoma.
Liposarcoma is rare in the pediatric population. Liposarcomas can be roughly divided into the following four large groups:
- Atypical lipomatous neoplasm/well-differentiated liposarcoma. These tumors do not metastasize unless they undergo dedifferentiation.
- Myxoid liposarcoma. Pure myxoid liposarcomas are characterized by a t(12;16)(q13;p11) translocation and can metastasize but usually have an excellent outcome in the absence of a round cell component.
- Dedifferentiated liposarcoma.
- Pleomorphic liposarcoma.