While additional loci (for example, NCRNA00173, LGR6, TFF3 and CBFA2T3, MMP17; Fig. 3b) may also contribute to the oestrogen-dependent tumour suppressor activity of RUNX1 in breast cancer, the role of AXIN1 downstream of RUNX1 in this context is strongly supported by deregulation of β-catenin in RUNX1-deficient ER+ breast cancer cells and the corrective effects of IWR1. The gene discussed is MMP17; the disease is breast cancer.