Acidic extracellular pH is maintained in cancer cells through the increased expression or activity of plasma membrane ion transporters and intracellular pH regulators, including the Na+/H+ exchanger 1 (NHE1), carbonic anhydrases, monocarboxylate transporter 1 and 4, and Na+-driven HCO3− exchangers [31]. This evidence concerns the gene SLC9A1 and cancer.