SLC16A1 and cancer: On the other hand, MCT1 is independent of hypoxia, activated in response to exogenous lactate, and can equally operate in both directions, enabling the export of intracellular lactate produced by glycolysis (in both anaerobic and aerobic conditions) as well as the import of extracellular lactate as a source of energy for the oxygenated cancer cells (Sonveaux et al., 2008).