ESR1 and breast cancer: PIK3CA-mutant ER+ primary human breast cancers exhibited increased Wnt target gene, receptor and ligand mRNA expression [25,96].PIK3CAH1047R expression increased activated-β-catenin and Wnt target gene expression in ER+ mouse mammary tumor cells [99].PIK3CAH1047R or PIK3CAE545K expression increased activated-β-catenin in mouse mammary glands [99].