High levels of the steroid transporting OATPs (i.e., OATP1A2, OATP2B1, OATP1B3, OATP4A1, OATP4C1) have been suggested for breast cancer cells, as compared to normal tissue (Pizzagalli et al., 2003; Al Sarakbi et al., 2006; Meyer zu Schwabedissen et al., 2008; Wlcek et al., 2008). Here, SLCO1A2 is linked to breast cancer.