SLC9A1 and breast cancer: Among hormones, growth factors and cytokines that have been shown to be protumoral, either in BC or in other solid tumors, apart from estrogens, human growth hormone (hGH), prolactin, insulin and EGF and its receptor, are VEGF, PDGF, certain interleukins and sex steroids, some of which up-regulate NHE1 (Figure 1) [8].