In 2015, the U.S. Food and Drug Administration (FDA) granted approval for palbociclib in combination with letrozole, a third-generation aromatase inhibitor, as first-line therapy for postmenopausal women with HR+/HER2-advanced breast cancer (Pernas et al., 2024; Finn et al., 2015). This evidence concerns the gene ERBB2 and breast cancer.