SLC9A1 and neoplasm: Transport proteins such as NHE1 effectively extrude these protons10 thereby contributing to the typical acidification of solid tumours.Their (over-)expression or activation correlates with the malignancy of tumourcells10, 11, 27 so that proteins involved in intra- andextracellular pH regulation are important candidates in regulating the metastaticbehaviour of tumour cells.