Evidence includes the preferential expression of MCT4 in the hypoxic/glycolytic cancer cell compartment and of MCT1 in well-oxygenated tumor areas, as well as the observation that 13C-labelled lactate can be converted into downstream metabolites of the lactate oxidative pathway (such as 13C-alanine) in tumors in vivo [20]. The gene discussed is SLC16A3; the disease is cancer.