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.