SLCO4A1 and breast cancer: Therefore, several previous studies have investigated the expression of uptake carriers for sulfated steroids in the normal mammary gland and breast cancer tissue, including OATP1A2, OATP2B1, OATP3A1, OATP4A1, and OATP1B3 (Pizzagalli et al., 2003; Miki et al., 2006; Meyer zu Schwabedissen et al., 2008; Wlcek et al., 2008; Kindla et al., 2011; Banerjee et al., 2014).