However, de Gooijer et al. (2021) and other groups have demonstrated that “ATP-binding cassette transporters restrict drug delivery and efficacy against brain tumors even when blood-brain barrier integrity is lost,” suggesting that ABCB1 and ABCG2 overcome barrier leakage (Thomas et al., 2009; Adkins et al., 2013; Dudek et al., 2013; Li et al., 2013; Ballard et al., 2016; Vaidhyanathan et al., 2016; Yang et al., 2016; Gampa et al., 2018, 2019; Ippen et al., 2019). Here, ABCG2 is linked to brain neoplasm.