Expression of cytokeratins in gliomas

Metastatic carcinoma, which is a common malignant tumor seen in the central nervous system is often difficult to distinguish from glioblastoma multiforme. In general, neoplastic cells maintain fidelity in the expression of parent cell intermediate filament and immunohistochemistry remains the mainstay in diagnosis. A panel consisting of GFAP (usually positive for astrocytic tumors) and cytokeratin (usually positive for metastatic carcinomas) is most commonly used for this purpose. However, co-expression of two or more classes of intermediate filament proteins by neoplasms is a widespread phenomenon and there are reports of glial neoplasms expressing keratin markers. Our aims and objectives were to analyse the expression of both cytokeratin and GFAP in different glial tumors and metastatic carcinomas. Cases were collected for a period of two years. All the cases were diagnosed as primary or metastatic intracranial tumors. Formalin-fixed paraffin-embedded thin sections were taken on egg-albumin coated slides and immunostaining with GFAP and polyclonal cytokeratin was done. Forty-five tumors were analysed, including 35 glial neoplasms and 10 metastatic carcinomas of which 7 of the 32 astrocytic neoplasms (22%) showed focal immunoreactivity with pancytokeratin. All of the glial tumors but none of the metastatic carcinomas were positive with GFAP. So our conclusion was that co-expression of GFAP and CK is a fairly common phenomenon, especially in case of undifferentiated and high grade gliomas and this must be kept in mind while differentiating these cases from metastatic carcinoma, as CK positivity does not rule out the diagnosis of a glial neoplasm. Further studies with an expanded panel of CK is most useful for this.