The immunophenotype of hemangiopericytomas and glomus tumors, with special reference to muscle protein expression: an immunohistochemical study and review of the literature.

Glomus tumors and hemangiopericytomas have traditionally been described as neoplasms of pericytes. Ultrastructurally, smooth muscle features have been identified in the cells of the glomus tumor, while the cells of the hemangiopericytoma have been described as more closely resembling normal pericytes. Immunocytochemical studies were performed to demonstrate the immunophenotype of these two tumors and to particularly evaluate expression of muscle-specific actin and desmin. Using the avidin-biotin immunoperoxidase method, formalin-fixed, paraffin-embedded tissue from 16 glomus tumors and 11 hemangiopericytomas was evaluated for the presence of vimentin, low-molecular-weight cytokeratins (35 beta H11), muscle actins (HHF35), desmin (clone 33), S100 protein, nerve growth factor receptor (NGFR5), myelin-associated glycoprotein (CD57), Factor VIII-related antigen, and Ulex lectin. Muscle actins were found in 14 of 16 tumors, and desmin was found in three of 16 of the glomus tumors. None of the 11 hemangiopericytomas expressed either desmin or muscle actins. Variable numbers of both tumors were positive with antibodies to CD57, with the nerve growth factor receptor, and with antibodies to S100 protein. In conclusion, these studies provide immunocytochemical evidence of smooth muscle differentiation in glomus tumors. Although muscle differentiation has been identified in the normal pericyte by expression of muscle-specific actin (HHF35), we find no evidence for analogous differentiation in the population of cells comprising hemangiopericytomas.