Palbociclib has been assessed in two phase III studies: PALOMA-2 (assessing palbociclib + letrozole vs. placebo + letrozole) and PALOMA-3 (assessing efficiency of palbociclib + fulvestrant vs. placebo + fulvestrant) in women with HR+/HER2− metastatic BC who progressed after endocrine therapy [87,91]. The gene discussed is HR; the disease is breast cancer.