The LUZERN trial was a multicenter, open-label, phase II clinical trial that assessed the efficacy and safety of niraparib plus aromatase inhibitors (AIs) for patients with pretreated hormone receptor-positive/HER2-negative (HR[+]/HER2[−]) advanced breast cancer harboring a gBRCAm (cohort A) or who exhibited germline BRCA1/2 wild-type (gBRCAwt) and HRDs based on the Myriad myChoice® CDx PLUS test developed by Myriad Genetic Laboratories, Inc., Salt Lake City, UT, USA) (exploratory cohort B). This evidence concerns the gene CYP19A1 and breast cancer.