Heterogeneity in the expression of markers for drug resistance in brain tumors.

Brain tumors, in general, display a multidrug-resistant phenotype. This study evaluated the immunohistochemical expression and distribution of P-glycoprotein (Pgp), multidrug resistance protein (MRP1), lung resistance protein (LRP) and O6 methylguanine-DNA methyltransferase (MGMT) in low- and high-grade astrocytoma, oligodendroglioma and in different subgroups of meningioma. The results revealed a marked heterogeneity in the expression and distribution among the analyzed tumors. In astrocytoma and oligodendroglioma, Pgp and MRP1 were observed in the capillary endothelium and in scattered tumor cells, whereas LRP occurred only in tumor cells. A pronounced expression of MGMT was found independent of the histopathological grade. An enhanced expression of MRP1 and LRP in astrocytoma and oligodendroglioma were more often evident in older patients (> 50 years). Survival analysis suggested a markedly decreased overall survival for patients suffering from low-grade glioma overexpressing Pgp. In meningioma, a heterogeneous expression of Pgp, MRP1, LRP and MGMT was seen with the most prominent staining localized to the capillary endothelium. Pgp was significantly more often overexpressed (p < 0.05) in transitional compared to meningothelial meningioma. The marked heterogeneity in the expression suggests that analysis of these factors can be of importance in the selection of individualized chemotherapy, regardless of tumor type.