Malignant peripheral nerve sheath tumors with t(X; 18). A pathologic and molecular genetic study

Spindle cell sarcomas often present the surgical pathologist with a conside rable diagnostic challenge. Malignant peripheral nerve sheath tumor, leiomy osarcoma, fibrosarcoma, and monophasic synovial sarcoma may all appear simi lar histologically. The application of ancillary diagnostic modalities, suc h as immunohistochemistry and electron microscopy, may be helpful in the di fferentiation of these tumors, but in cases in which these adjunctive: tech niques fail to demonstrate any more definitive evidence of differentiation, tumor categorization may remain difficult. Cytogenetic and molecular genet ic characterization of tumors have provided the basis for the application o f molecular assays as the newest components of the diagnostic armamentarium . Because the chromosomal translocation t(X;18) has been observed repeatedl y in many synovial sarcomas, it has been heralded as a diagnostic hallmark of synovial sarcoma To formally test the specificity of this translocation for the diagnosis of synovial sarcoma, RNA extracted from formalin-fixed, p arrafin-embedded tissue from a variety of soft tissue and spindle cell tumo rs was evaluated fbr the presence of t(X;18) by reverse transcriptase-polym erase chain reaction. Although 85% of the synovial sarcomas studied demonst rated t(X;18), 75% of the malignant peripheral nerve sheath tumors in our c ohort also demonstrated this translocation. We conclude that the translocat ion t(X;18) is not specific to synovial sarcoma and discuss the implication s of the demonstration of t(X;18) in a majority of malignant peripheral ner ve sheath tumors.