To elucidate the effect of HO-1 expression in the host on the progression of the tumor, we induced or suppressed the HO-1 expression/activity by using an HO-1 inducer, PEG-hemin, which is a nanoformulation of the typical HO-1 inducer hemin [21], or HO-1 inhibitor PEG-ZnPP, which is a polymeric micellar formation of the competitive HO-1 inhibitor ZnPP [32]. Here, HMOX1 is linked to neoplasm.