Mediators of increased acid extrusion in tumor cells include the Na+/H+ exchanger NHE1 (SLC9A1), the Na+,HCO3− cotransporter NBCn1 (SLC4A7), the lactate,H+ cotransporters of the monocarboxylate transporter family, MCT1 and MCT4 (SLC16A1 and −3), and, in some cells, V-type H+-ATPases [8, 12–14]. The gene discussed is SLC16A1; the disease is neoplasm.