Studies show over-expression of BMP-6 particularly in ER positive cell lines and tumour samples (Ong et al. 2004, Zhang et al. 2007), however, BMP-6 inhibits oestrogen-induced mitosis of ER positive breast cancer cells (Takahashi et al. 2008) and targeting BMP-6 in MCF-7 cells using shRNA knockdown promoted cell proliferation (Lian et al. 2013). Here, ESR1 is linked to breast cancer.