SLCO4A1 and glioblastoma: Quantification of the tissue-wide expression of each OATP isoform protein revealed a significant increase in the mean integrated intensity of OATP1A2 (6.1-fold, P < .0001), OATP2B1 (3.7-fold, P = .0106), OATP1C1 (12-fold, P = .0001), and OATP4A1 (4-fold, P = .0005) in GBM tumor tissue compared to non-tumor tissue (Figure 1A).