ABCC1 and neoplasm: In addition, the fact that MRP1 has been shown to be highly expressed in high grade glioma patient samples (Benyahia et al., 2004), with localization of MRP1 to the luminal side of brain capillary endothelial cells (Nies et al., 2004) suggests that the efficient efflux action of MRP1 in the GBM tumor microenvironment may contribute to the highly resistant nature of GBM tumors to current chemotherapeutics.