Besides playing an important role in multidrug resistance of cancer cells, ABCG2 is expressed, i.e., in the apical membrane of intestinal epithelial cells, the canalicular membrane of hepatocytes, and at the placental-fetal interface, where it reduces uptake and tissue-specific disposition of drugs that serve as substrates of the ABC transporter (Allikmets et al., 1998; Ni and Mao, 2011; Zolk and Fromm, 2011; Stacy et al., 2013; Schumacher and Benndorf, 2017). Here, ABCG2 is linked to cancer.