SLCO1C1 and glioblastoma: Furthermore, the mean average intensity of OATP1A2 (6-fold, P < .0001), OATP2B1 (6-fold, P < .0001), OATP1C1 (7-fold, P = .0001) and OATP4A1(4-fold, P = .0004) in GBM blood vessels was significantly higher than in non-tumor blood vessels (Figure 3M–P).