Sodium homeostasis in the tumour microenvironment.

The concentration of sodium ions (Na) is raised in solid tumours and can be measured at the cellular, tissue and patient levels. At the cellular level, the Na gradient across the membrane powers the transport of H ions and essential nutrients for normal activity. The maintenance of the Na gradient requires a large proportion of the cell's ATP. Na is a major contributor to the osmolarity of the tumour microenvironment, which affects cell volume and metabolism as well as immune function. Here, we review evidence indicating that Na handling is altered in tumours, explore our current understanding of the mechanisms that may underlie these alterations and consider the potential consequences for cancer progression. Dysregulated Na balance in tumours may open opportunities for new imaging biomarkers and re-purposing of drugs for treatment.