Breast cancer. Iron-induced ROS formation in human breast cancer cells is supported by increased activity of heme oxygenase (HO-1) and consequently by increased expression of metalloproteinase-1 (MMP-1), suggesting a potential link between iron overload related to estrogen metabolism and cancer metastasis (Liou and Storz, 2010[275]). The gene discussed is HMOX1; the disease is breast cancer.