To directly test a role of differentiated macrophage-derived HO-1 in regulation of tumor development, we inoculated PC3 cells with bone marrow derived macrophages (BMDM) expressing HO-1 (PC3+Hmox1flfl) or lacking HO-1 (PC3+LyzM-Cre:Hmox1flfl) into the flanks of nude mice. The gene discussed is HMOX1; the disease is neoplasm.