Jiang et al (2007) showed that CYP epoxygenase overexpression enhanced tumour metastasis of MDA-MB-231 human breast carcinoma cells to the lungs of athymic BALB/C mice. Moreover, CYP epoxygenase overexpression or EET treatment markedly enhanced the migration, invasion, and prometastatic gene expression profiles in a variety of cancer cell lines in vitro (Jiang et al, 2007). Functional polymorphisms of CYP2C8 and CYP2C9 may thus be of importance for breast cancer risk, tumour characteristics, and treatment response. This evidence concerns the gene CYP2C9 and breast cancer.