Some of them are even expressed in breast cancer tissue or breast cancer cell lines, including OATP1A2, OATP1B3, OATP2B1, OATP3A1, OATP4A1, and others, thus making them candidates for steroid sulfate uptake in breast cancer (Pressler et al., 2011; Obaidat et al., 2012; Nakanishi and Tamai, 2014). Here, SLCO4A1 is linked to breast cancer.