The hydrogen sulfide (H2S)-generating enzymatic system composed of cysteine aminotransferase (CAT, EC 2.6.1.3, also known as aspartate aminotransferase, AST, or glutamate transaminase, GOT), and 3-mercaptopyruvate sulfurtransferase (MST, EC 2.8.1.2), is known to be implicated in the catabolism of cysteine [13], but its role is far from being completely explored in cancer. This evidence concerns the gene CAT and cancer.