HMOX1 and neoplasm: The role of HMOX1 in tumor cell proliferation is controversial: its expression in tumors was found very frequently up-regulated and a role for HMOX1 as a mediator of ROS-promoted cell proliferation was established; on the other hand, however, in other kinds of tumors an HMOX1 anti-proliferative action was demonstrated, often associated to effects mediated by CO and biliverdin (99, 101).