Neural differentiation in small round cell tumors of bone and soft tissue with the translocation t(11;22)(q24;q12): an immunohistochemical study of 11 cases.

Clinical, cytogenetic, histopathologic, and immunohistochemical data were obtained in a series of 11 small round cell tumors (SRCT) of bone and soft tissue with the translocation t(11;22) (q24;q12). Ten cases were primary in bone, and one was of extraskeletal origin. According to conventional histopathologic criteria, 10 cases were Ewing's sarcomas (ES) and one was a peripheral neuroectodermal tumor (PNET). Besides the t(11;22), six cases had additional chromosomal aberrations, including trisomy 7 and partial trisomy for the long arm of chromosome 1, which have both been described as nonspecific secondary abnormalities often associated with tumor progression. The tumors were screened for neural differentiation with an antibody panel consisting of neuron-specific enolase, S100 protein, Leu-7, chromogranin, synaptophysin, and neurofilament. Three cases of ES were positive for S100 protein. The PNET and one case of ES were positive for neuron-specific enolase. All of the remaining immunohistochemical stains were negative. Hence, five of 11 SRCT of bone or soft tissue with the t(11;22) showed morphologic and/or immunohistochemical evidence of neural differentiation. In this limited series of cases, no cytogenetic or prognostic differences could be demonstrated between cases with and without a neural phenotype. Our results support the hypothesis that SRCT of bone of soft tissue with the t(11;22) form a single biologic entity displaying varying degrees of neuroectodermal differentiation. The clinical significance of additional cytogenetic abnormalities and of morphologic or immunohistochemical evidence of neural differentiation in this group of tumors needs to be further studied.