HMOX1 and melanoma: We found that: (1) females grew much smaller tumors than males after both intracutaneous and intravenous injection with melanoma cells, (2) growth of primary tumors and lung nodules was completely inhibited in HO-1+/+ females, which was associated with the augmented leukocyte infiltration of primary tumors with lymphocytes T as a major subpopulation, and (3) HO-1+/− and HO-1−/− males formed bigger primary tumors and more numerous lung nodules than their wild-type counterparts, as well as more of them showed micrometastases in liver and spleen.