In the phase III PALOMA-2 and -3 trials, first- or subsequent-line palbociclib plus endocrine therapy (ET) treatment significantly improved progression-free survival (PFS) compared with ET alone in patients with hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2–) advanced breast cancer (ABC) [3–5]. Here, ERBB2 is linked to breast cancer.