Characteristics and Clinical Outcomes of BRCA Germline Mutation Carriers with Advanced Breast Cancer Treated with PARP (Poly ADP-Ribose Polymerase) Inhibitors: A Single-Institution Experience.

Background/Objectives: Several trials have highlighted the importance of PARP inhibitors (PARPi) in the treatment of BRCA-associated breast cancers (BC), initiating changes in practice. However, data on the real-life outcomes of PARPi therapy is limited. In this study, we characterized the clinical characteristics and outcomes of patients with advanced BC and germline BRCA pathogenic variants (PVs) who received PARPi therapy. Methods: We conducted a retrospective single-institution cohort study of patients with advanced BC and germline BRCA1/2 PVs treated with PARPi. Outcomes included objective response rate (ORR), progression-free survival (PFS), and overall survival (OS). Survival was estimated using Kaplan-Meier methods, and prognostic factors were evaluated using Cox regression analysis. Results: Of the 107 patients treated with PARPi, 48 (44.9%) and 59 (55.1%) had BRCA1 and BRCA2 PVs, respectively. Ninety-seven patients (90.7%) had invasive ductal carcinoma and 42 (39.3%) had triple-negative BC. Nineteen (17.8%) patients had de novo metastatic BC. Sixty-two (57.9%) patients received at least one line of systemic therapy before PARPi; 24 (22.4%) patients received prior platinum. ORR was 62.6%, and the median duration of response (DoR) was 7 months (range, 2.1-96.2). The median PFS was 9 months (95% CI, 6.9-10.5) and median OS was 25.8 months (95% CI, 18.7-31.5). In multivariable models for PFS, bone metastases (HR = 2.25; 95% CI, 1.40-3.61; p = 0.0008) and lung metastases (HR = 2.40; 95% CI, 1.45-3.98; p = 0.0007) were independently associated with increased risk of progression or death. In multivariable models for OS, brain metastases (HR = 3.54; 95% CI, 1.59-7.90; p = 0.0020), bone metastases (HR = 2.22; 95% CI, 1.27-3.88; p = 0.0050), and lung metastases (HR = 2.38; 95% CI, 1.38-4.11; p = 0.0018), were independently associated with increased risk of death. Conclusions: The clinical outcomes of our real-world patients are similar to those reported in previous clinical trials. In addition, metastatic site distribution was independently prognostic for survival outcomes and may support baseline risk stratification at the time of PARPi initiation. Further studies of predictive markers of response and resistance, as well as sequencing with platinums and combinations with other targeted agents, are needed to optimize the benefits of PARPi in this patient population.