In cancer, H+-coupled transport by MCTs tends to drive lactate from the interstitium into tumor cells to maintain the concentration gradients of lactate and Ph [191,192], and they mold a phenomenon called “metabolic symbiosis” between hypoxic and aerobic carcinoma cells, where lactate secreted by glycolytic cancer cells is exported by MCT4 and transported into oxidative cancer cells by MCT1 as an oxidative fuel [188,193,194]. This evidence concerns the gene SLC16A3 and carcinoma.