MIC2 detection in tumors of bone and adjacent soft tissues

The diagnosis of Ewing's sarcoma has been based classically in large part on the exclusion of other similar small round-cell tumors by light microscopic and histochemical criteria. This study was undertaken to explore the use of a recently developed immunohistochemical stain directed against the glycoprotein p30/32MIC2 antigen (the gene product of MIC2), as a diagnostic tool and as a probe for the examination of potential interrelationships among the putative members of the family of peripheral primitive neuroectodermal tumors. Fifty-six small round-cell tumors of bone were selected for study from the files of the Armed Forces Institute of Pathology and Rhode Island Hospital; all tissues had been formalin fixed and paraffin embedded. Nine of 10 Ewing's sarcomas were MIC2 positive, as were 2 of 3 atypical Ewing's sarcomas (small round-cell tumors that diverged from the classic pattern of Ewing's sarcoma by exhibiting a greater degree of cytologic atypia and pleomorphism), and 7 of 8 Askin tumors of the thoracopulmonary region. Ten of 11 mesenchymal chondrosarcomas, 1 primitive neuroectodermal tumor of bone, 10 small cell osteosarcomas, 10 malignant lymphomas, and 3 sarcomas of bone (not additionally subclassified) were negative. The finding of MIC2 positivity in the majority of Ewing's sarcomas and Askin tumors provides additional support for earlier proposals (based on a shared cytogenetic abnormality, among other criteria) that these lesions be considered members of the same family, the peripheral primitive neuroectodermal tumors. The present study, drawing on archival and current case material (including decalcified and undecalcified specimens), indicates that neither the specimen age nor the application of any of a variety of decalcification solutions appears to adversely influence MIC2 staining of paraffin-embedded tissues. This suggests that this antibody has use in retrospective and prospective studies. The rare occurrence of false negative (in the case of Ewing's sarcoma) and positive results in tumors other than peripheral primitive neuroectodermal tumors (as in 1 of the mesenchymal chondrosarcomas) suggests that MIC2 staining should not be relied on as the sole criterion for identification or exclusion of Ewing's sarcomas and related tumors.