Immunoreactivity for Leu-7 in neurofibrosarcoma and other spindle cell sarcomas of soft tissue

Monoclonal antibodies to Leu-7 have been reported to recognize a constituent of myelin-associated glycoprotein. Because of this, the authors studied 20 cases of neurofibrosarcoma (NFS), 7 of leiomyosarcoma (LMS), 3 of fibrosarcoma (FS), 8 of malignant fibrous histiocytoma (MFH), 5 of monophasic spindle cell synovial sarcoma (MSS), 5 of neurilemmoma, and 5 of neurofibroma for Leu-7 reactivity, to determine its utility in differential diagnosis. Selected examples of each tumor type were also studied ultrastructurally. Leu-7 was compared with the expression of S-100 protein, myelin basic protein, desmin, cytokeratin, and epithelial membrane antigen in the 43 neoplasms. Fifteen examples of NFS, 2 of LMS, and 2 of MSS were Leu-7+; 2 neurofibromas and 4 neurilemmomas also demonstrated reactivity with this antibody. In contrast, all cases of FS and MFH were Leu-7-. Synovial sarcomas could be effectively separated from NFS by reactivities for cytokeratin and epithelial membrane antigen in the former, but not the latter, lesions. However, LMSs and NFSs demonstrated significant immunocytochemical overlap, including shared positivity for S-100, desmin, and myelin basic protein in several cases. These results suggest that Leu-7 has restricted utility in immunohistochemical diagnosis, and must be utilized only in concert with other antigens. Moreover, it would appear that in selected instances, smooth-muscle and neurogenic sarcomas must be separated on the basis of clinical, histopathologic, and ultrastructural features alone.