PIK3CA and breast cancer: Drugs that target CDK4/6 to inhibit cell cycle activation (Hortobagyi et al, 2016), PI3K‐inhibitors that target tumor with activating PIK3CA mutations (André et al, 2019), and MTOR‐inhibitors that prevent the activation of MTOR signaling and cell proliferation (Baselga et al, 2012) have been studied and approved for the treatment of advanced ER+ breast cancers in combination with endocrine therapy.