HMOX1 and breast cancer: In 2009, Kim et al. showed that 15-Deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2), an endogenous ligand of PPARγ, could upregulate the expression of haem oxygenase-1 (HO-1), level of ROS and subsequently expression of matrix metalloproteinase-1 in human breast cancer cells, and increased metastasis and invasiveness.