The relative contribution of PI3Kα/β/γ/δ isoforms to Wnt/β-catenin down-regulation in ER− breast cancer is also unknown and should be investigated in future studies using isoform-specific deletion or small molecule inhibition, particularly as PI3Kβ plays a critical role in PTEN-null ER− breast cancer [50–53]. This evidence concerns the gene PTEN and breast cancer.