ESR1 and breast cancer: The phase III AFT-38 PATINA trial demonstrated that adding the CDK4/6 inhibitor palbociclib into a regimen of anti-HER2 therapy (trastuzumab with or without pertuzumab) and endocrine therapy (with an aromatase inhibitor or fulvestrant) significantly extended PFS in patients with ER+, HER2 + metastatic BC following induction chemotherapy.