Finally, as shown in Fig. 2g, SOX2 mRNA was markedly elevated in biopsies from RUNX1-mutant versus RUNX1-WT human primary breast tumours in the clinical cohort of Ellis et al.18 Thus, deregulation of β-catenin in RUNX1-deficient ER+ breast cancer might contribute to disease progression by promoting cell growth in general and expansion of a stem cell-like population in particular. Here, RUNX1 is linked to breast cancer.