Patterns of epithelial metaplasia in malignant gliomas. II. Squamous differentiation of epithelial-like formations in gliosarcomas and glioblastomas.

Six cases are reported (four gliosarcomas and two glioblastomas) in which the epithelial-like areas of glial anaplasia showed focal squamous cell differentiation, characterized by the development of epithelial whorls, keratin pearls and immunopositivity for cytokeratin. The expression of glial fibrillary acidic protein and the development of squamous metaplasia usually were mutually exclusive. Autopsy findings in two patients and clinical work-up in five failed to disclose a primary extraneural malignancy. It is suggested that squamous differentiation may represent an extreme form of epithelial metaplasia in a malignant glioma. This possibility should be kept in mind in the diagnostic evaluation of such cases, especially in view of the current emphasis on the immunomorphologic demonstration of intermediate filament tumor markers.