The recently published study of Flonta et al (2009), which was published during the preparation of this paper, identified endogenous Mb in various human cancer cell lines and human epithelial tumours including breast cancer and elucidated several signals, including NO, oxidative stress and mitogens (EGF and serum growth factors) and also hypoxia, that were able to stimulate Mb expression in cultivated MCF7 breast cancer cells. Here, EGF is linked to breast cancer.