AXIN1 and breast cancer: That RUNX1 regulates AXIN1 in an oestrogen-dependent manner in vivo is suggested by (1) the decreased Axin1 expression in the predominantly ER+ ML cells, but not in the predominantly ER− LP cells in Runx1-deficient versus control murine mammary epithelium (Fig. 4e), (2) the positive correlation between AXIN1 mRNA and the RUNX1 inhibitory index in ER+ but not ER− breast cancer subtypes in TCGA (Fig. 5a) and (3) the positive correlation between RUNX1 and AXIN1 protein levels in ERhigh but not ERlow human ER+ breast cancer tumours (Fig. 5b).