HMOX1 and cancer: HO1 is also the rate-limiting enzyme in heme catabolism by degrading heme into iron, carbon monoxide and the endogenous antioxidants biliverdin/bilirubin [49], which has a cytoprotective role to conquer the oxidative stress induced by chemotherapeutic agents in tumor cells, thus preventing the cancer cells from apoptosis and autophagy [50, 51].