EZH2 and breast cancer: It has been shown that the growth of BRCA1-deficient mouse mammary tumours is dependant on EZH2 expression.18 Conversely, EZH2 inhibition in breast cancer cell lines can cause BRCA1 nuclear exportation and inactivation.19 Crucially, BRCA1 interacts directly with EZH2 in both mouse embryonic stem cells and human breast cancer cells, functioning as a negative modulator of EZH2 activity.20