Metabolic symbiosis between cancer cells and CAFs requires that the cells express a subtype of monocarboxylate transporter 1 (MCT1), which contributes to the uptake of lactate provided by CAFs expressing MCT4.30 Cancer shows a high metabolic heterogeneity; MCT4-expressing tumor cells produce and secrete lactate from glycolysis, while MCT1-expressing cancer cells import lactate via MCT1 and perform oxidative phosphorylation.31 Cancer cells synthesize pyruvate from lactate, providing the tricarboxylic acid cycle with intermediate metabolites. The gene discussed is SLC16A1; the disease is neoplasm.