Immunohistochemical study of anaplastic meningioma with special reference to the phenotypic change of intermediate filament protein.

The phenotypic changes in the transformation of classic or atypical meningioma to anaplastic meningioma were investigated. Among nine patients with anaplastic meningioma, four men and five women ranging in age from 32 to 75 years, four cases were identified as anaplastic meningioma at the first operation (de novo type), while five cases were identified as classic or atypical meningioma at the first operation but at recurrence had transformed to anaplastic meningioma (secondary type). Immunohistochemical analysis was performed with the avidin-biotin complex method using monoclonal antibodies for glial fibrillary acidic protein, cytokeratin, alpha-internexin, neurofilament proteins (70 kd, 168 kd, and 200 kd), desmin, vimentin, CD34, Ki-67, epithelial membrane antigen, and S-100 protein. Immunohistochemical analysis showed positive immunoreactivity for cytokeratin, alpha-internexin, neurofilament proteins, vimentin, and glial fibrillary acidic protein during the course of progression. Expression of epithelial membrane antigen decreased with malignant progression. Marked expression of cytokeratin was observed in anaplastic meningioma. Ki-67 labeling index increased at every recurrence of both the de novo and secondary types. The major phenotypic changes in the transformation of meningioma from the classic to the anaplastic type are loss of meningioma architecture, decreased expression of epithelial membrane antigen, increased expression of vimentin, and metaplastic expression of alpha-internexin and neurofilament triplet proteins.