ABCB1 and neoplasm: In tumor cells and at the blood-brain barrier, ABCB1 and ABCG2 restrict the uptake of anticancer drugs, and transporter expression levels were thought to correlate with the extent of multidrug resistance (Marchetti et al., 2008; Agarwal et al., 2010, 2011; de Vries et al., 2012; Laramy et al., 2017; de Gooijer et al., 2018c).