CD34 immunoreactivity in nervous system tumors.

CD34 is a sialylated transmembrane glycoprotein of unknown function that is present in myeloid progenitor cells, endothelial cells, and some fibroblast-related mesenchymal cells. However, its tissue distribution is still incompletely characterized. In this study we evaluated the distribution of CD34 antigen in tumors of the central and peripheral nervous system. For comparison the tumors were also stained for CD31, also known as platelet-endothelium cell adhesion molecule (PECAM-1), a transmembrane glycoprotein so far considered to be endothelium specific beyond its reactivity with certain hematopoietic cells. Neurofibromas showed consistently high numbers of CD34-positive spindle cells, whereas peripheral and acoustic schwannomas were negative. A subset of meningiomas (15%) showed CD34-positive tumor cells, and some were also weakly positive for CD31. Gliomas were negative. Meningeal hemangiopericytomas were consistently CD34 positive, but CD31 negative. These results indicate a moderately widespread distribution of the CD34 antigen in nervous system tumors, and necessitate caution in making conclusions regarding endothelial cell differentiation of nervous system tumors on the basis of CD34 immunoreactivity.