RecruitingPhase 2Drug trialPALbociclib Endocrine Therapy Followed by Talazo Vs. Talazoz-Atezo StudyThis study is a prospective, two-arm, randomized phase II study of talazoparib versus talazoparib plus atezolizumab in ER+ premeonopausal women with metastatic breast cancer harboring HRD scar 1st line treatment: GnRH agonist + Aromatase Inhibitor(AI) + Palbociclib 28 days after the last treatment of 1st line treatment(., randomization for 2nd line treatment is conducte to arm A(Talazoparib+Atezolizumab) and arm B(Talazoparib monotherapy)