ERBB2 and breast cancer: The cyclin-dependent kinase 4/6 (CDK4/6) inhibitor palbociclib, in combination with endocrine therapy (ET), significantly prolonged progression-free survival in women with hormone receptor–positive, human epidermal growth factor receptor 2–negative advanced breast cancer (HR+/HER2− ABC) in PALOMA-2 and PALOMA-3.