HMOX1 and cancer: HO-1, as the initiating and rate-limiting enzyme of haem catabolism, can catalyse the conversion of haem to biliverdin, carbon monoxide, and iron (Zhang et al., 2018a), so HO-1 may be a potential source of intracellular iron on which ferroptosis depends and is beneficial for cancer therapy (Adedoyin et al., 2018).