role of glial fibrillary acidic protein [gfap] in the diagnosis of neuroepithelial tumors

ABSTRACT

The aims of this study are to identify the Immunohistochemical [IHC] expression of Glial Fibrillary Acidic Protein [GFAP] in different types of neuroepithelial tumors in Mosul city and to correlate the results with grade of tumor, with the results of other studies and to assess the diagnostic role of GFAP in the diagnonsis of neuroepithelial tumors and their differentiation from neuroglial tumors. This study included 56 cases of neuroepithelial tumors. 22 cases were collected during the period extending from October 2007 to May 2008. [The rest of the cases were retrieved from a filing system extending back to 2004]. In addition to two miscellaneous tumors, [one meningioma and the other secondary adenocarcinoma]. All cases were obtained from Al- Jamhuri Teaching Hospital in the western side of Mosul City, Northern Iraq and some private laboratories. Typing and grading of the tumors were done according to World Health Organization [WHO] classification system. IHC procedure was done for GFAP using polyclonal antibodies and chromogen visualizing system. A semi-quantitative histochemical score was used to record the results of GFAP staining according to the system established by Catherine L. Nutt et al. Thirty seven cases were diagnosed as astrocytoma, while 8 cases out of ependymoma, 4 cases of oligodendroglioma, and three cases medulloblastoma were shown. In addition, this study revealed that one case for each of oligoastrocytoma, Medulloepithelioma, atypical rhabdoid tumor and astroblastoma. Glial Fibrillary Acidic Protein [GFAP] was expressed in 85.7% of neuroepithelial tumors. Higher GFAP positivity was found in glioma than other types of neuroepithelial tumors [P value <0.05]. On the other hand, GFAP was expressed in [36%] of astrocytoma. In oligodendroglioma, 3 cases out of 4 were positive while all cases of ependymoma were positive. In addition, oligoastrocytoma was positive while the remaining cases of neuroepithelial tumors were negative. In general, each type of glioma had special staining pattern of GFAP. GFAP status was found to be inversely related with the grade of glioma [P value <0.05]. GFAP is expressed more frequently in glioma than in other neuroepithelial tumors and this result is similar to many other studies done outside Iraq and it is correlated inversely with the grade of tumor. So, it is a valid supplementary diagnostic procedure for neuroepithelial tumors and a reliable marker to differentiate between glial from non-glial tumors on one hand and between different types of glial tumors on the other hand