While the reasons for the presence of a larger proportion of de novo A/MBC patients in our study population is unclear, we suspect that patients with de novo metastatic disease may be more likely to be treated with palbociclib plus an aromatase inhibitor, while patients who progressed to A/MBC may be more likely to be treated with palbociclib plus fulvestrant. The gene discussed is CYP19A1; the disease is metastatic neoplasm.