The tricarboxylic acid (TCA) cycle, the “engine” of mitochondria, is sustained in cancer by a high uptake of the non-essential amino acid glutamine [55], which is converted to glutamate by glutaminases and subsequently is converted to α-ketoglutarate (α-KG) by either glutamate dehydrogenases or aminotransferases [56]. This evidence concerns the gene GLS and cancer.