XPR1 and breast cancer: XPR1 is the only identified transporter with Pi efflux as the primary function, but there are many examples of Na+-independent Pi transport processes that are not known to be mediated by XPR1 in non-erythroid mammalian cells, including Caco2BBE (Candeal et al., 2014), vascular smooth muscle (Villa-Bellosta et al., 2007; Hortells et al., 2020), articular chondrocytes (Solomon et al., 2007), brain endothelial cells (Dallaire and Béliveau, 1992), and breast cancer cells (Lacerda-Abreu et al., 2019; Lacerda-Abreu et al., 2020).