The electroneutral Na+, HCO3–-cotransporter NBCn1 (Slc4a7) is upregulated in human and murine breast cancer tissue compared to normal breast tissue; and acting in parallel with the Na+/H+-exchanger isoform 1 (NHE1, Slc9a1), NBCn1 is the predominant path for net acid extrusion from breast cancer cells [8,9,10,11]. The gene discussed is SLC9A1; the disease is breast cancer.