Niraparib Plus Aromatase Inhibitors for Luminal-like(HER2-,ER+) and gBRCA or HDR+ Metastatic Breast Cancer (LUZERN)

This is a Multicenter, Open-label, Phase II Clinical Trial to Evaluate the Efficacy and Safety of Niraparib plus Aromatase Inhibitors for Hormone Receptor (HR)-positive/Human Epidermal Growth Factor Receptor 2 (HER2)-negative Metastatic Breast Cancers with either Germline BRCA-mutated or Germinal BRCA-wild-type and Homologous Recombination Deficiency (HRD). The main objetive is to assess the efficacy -as determined by the clinical benefit rate (CBR)- of niraparib in combination with AIs in unresectable locally advanced or metastatic HR-positive/HER2-negative breast cancer patients harboring either gBRCAms or gBRCAwt and HRD. Upon meeting all selection criteria, patients enrolled in the study will receive the combination of niraparib orally (according to baseline criteria described in Table 4), once daily, flat- fixed, continuously in 28-day cycles and AI that must be identical to the last AI-containing regimen. A total of 23 patients will be recruited as follows: * Stage I: N=6 patients in the cohort A; * Stage II: N=8 patients in the cohort A; N=9 patients in the exploratory cohort B The total duration of the study period is 36 months follow until 5 years of follow up.