DIAGNOSTIC AND BIOLOGICAL IMPLICATIONS OF MEL-CAM EXPRESSION IN MESENCHYMAL NEOPLASMS

Mel-CAM (previously MUC18) is an integral membrane glycoprotein involv ed in heterophilic intercellular adhesions. Mel-CAM is expressed speci fically in certain normal mesenchymal tissues, including smooth muscle , endothelium, and Schwann cells. As a member of the immunoglobulin su pergene family of cell adhesion molecules (CAMs), Mel-CAM may play a p ivotal role in the normal differentiation and functional activity of t hese tissues. To determine the distribution of Mel-CAM in mesenchymal neoplasms and to investigate its potential role as a factor in tumor p rogression, we evaluated a spectrum of mesenchymal neoplasms by immuno histochemistry using a Mel-CAM-specific polyclonal antibody on formali n-fixed tissues. Mel-CAM positivity was observed in 5 (100%) of 5 leio myomas, 29 (91%) of 32 leiomyosarcomas, 5 (100%) of 5 hemangiomas, 5 ( 100%) of 5 angiosarcomas, 3 (100%) of 3 Kaposi's sarcomas, 8 (100%) of 8 schwannomas, 10 (100%) of 10 neurofibromas, 0 (0%) of 8 malignant p eripheral nerve sheath tumors, 2 (15%) of 13 malignant fibrous histioc ytomas, 0 (0%) of 8 fibrosarcomas, 0 (0%) of 7 synovial sarcomas, and 0 (0%) of 6 liposarcomas. These results show that Mel-CAM is expressed consistently in neoplasms of smooth muscle and vascular origin, and t hat immunostaining for Mel-CAM may serve as a useful adjunct in differ entiating leiomyosarcomas, angiosarcomas, and Kaposi's sarcomas from o ther spindle cell neoplasms. Furthermore, the observation that Mel-CAM is expressed consistently in schwannomas and neurofibromas but not in malignant peripheral nerve sheath tumors implicates Mel-CAM as a pote ntial modulator of malignant transformation in peripheral nerve tumors .