Some indications come from clinical studies on polymorphisms of the HO-1 promoter, in which the presence of less active allelic variants seems to correlate with a higher incidence of lung cancer or squamous cell carcinoma (SCC) in smokers or areca chewers, respectively [27,28], suggesting a protective role for HO-1 in cancer induction. Here, HMOX1 is linked to lung carcinoma.