We addressed this fundamental question by using two tumorigenic cancer cell lines, derived from human colon adenocarcinoma (LS174T) and mouse B16-F10 melanoma, in which we genetically disrupted the Warburg effect at either one of the three fermentative glycolytic steps: (1) glucose 6 phosphate isomerase, (2) lactate dehydrogenase A, B or both A/B, and (3) lactate/H+ symporters monocarboxylate transporter (MCT) 1 and 4 (see Figure 1). This evidence concerns the gene LDHA and cancer.