To address whether EZH2 represses the mesenchymal gene expression programme through H3K27me3 in breast cancer cells we treated MCF-7 cells with a highly specific small molecule that inhibits EZH2 methyltransferase activity (GSK126, thereafter referred to as EZH2i) [20] and analyse whether the loss of H3K27me3 induced the activation of the mesenchymal gene expression programme. The gene discussed is EZH2; the disease is breast cancer.