In human and murine breast cancer tissue analyzed without stratification by molecular subtype, Na+,HCO3– cotransport activity is elevated and protein expression of the Na+,HCO3– cotransporter NBCn1 (SLC4A7) and monocarboxylate transporters MCT1 (SLC16A1) and MCT4 (SLC16A3) are upregulated compared to normal breast tissue (Boedtkjer, 2019; Boedtkjer et al., 2013; Lee et al., 2016; Lee et al., 2018; Lee et al., 2015). Here, SLC16A3 is linked to breast cancer.