The discovery of the TKTL1 gene as the basis of a novel mammalian specific oxygen-independent energy metabolism similar to the heterofermentative lactic acid bacteria enabled the reinterpretation of Warburg’s and Szent-Györgyi’s findings that the metabolic switch to an oxygen-independent energy metabolism is a protective metabolism in proliferative cells—in cancer cells and in normal cells [19,20]. Here, TKTL1 is linked to cancer.