RUNX1 and breast cancer: Furthermore, RUNX1 and CBFB mutationshave only been found in the luminal subtype of human breast cancers (Banerji et al., 2012; Cancer Genome Atlas Network, 2012; Ellis et al., 2012) and our data so far showed that the loss ofRunx1 appeared to lead to a reduction in the luminal population(Figure 3D–F), we therefore examinedthe role of RUNX1 in luminal MECs (from which luminal breast cancers mayoriginate).