Tumors take a great energy expenditure to grow and proliferate. Cancer cells are, in fact, addicted to the main fuel of cellular metabolism, glucose. The molecular machinery that degrades this sugar for energy (the so-called glycolytic enzymes) is overexpressed in tumor cells. But this is not the only characteristic that differentiates the metabolism of tumor cells from normal ones. In fact, tumorigenesis involves large metabolic changes in cells, encompassed under the concept of metabolic reprogramming.