Methods: LUZERN (NCT04240106) was a multicenter, open-label, Simon’s two-stage, phase II clinical trial evaluating the efficacy and safety of niraparib with aromatase inhibitors (AIs) for patients with HR-positive/HER2-negative advanced breast cancer with either a germline BRCA1/2 mutation (cohort A) or germline BRCA1/2 wild-type and homologous recombination deficiency (exploratory cohort B). The gene discussed is CYP19A1; the disease is breast cancer.