HMOX1 and papilloma: Such delay in induction of papilloma development was observed in animals with a normal level of HO-1 during the whole time course of the experiment (P < 0.05 for comparison of HO-1+/+ and HO-1+/− and P = 0.061 for comparison of HO-1+/+ and HO-1−/−, Kaplan–Meier test).