Background: Poly (ADP-ribose) polymerase inhibitors (PARPi) are approved for the treatment of germline BRCA mutated (gBRCAm) breast cancer (BC) patients in the adjuvant and metastatic settings. Several studies have explored the role of PARPi in the neoadjuvant setting both with and without chemotherapy. Here, we explore the efficacy and safety of neoadjuvant PARPi in early HER2-negative BC patients. Methods: We searched PubMed, Scopus, and the Cochrane Library databases for randomized (RCT) and non-randomized clinical trials (non-RCT) that reported the proportion of patients with pathological complete response (pCR) after neoadjuvant PARPi and safety. Statistical analysis was performed using R software. Data were pooled using the random effects model. Results: Analysis included 3 RCTs and 4 non-RCTs, with 942 HER-2 negative breast cancer patients, 293 harboring a gBRCA 1/2 mutation. In a pooled analysis, gBRCAm carriers achieved a significantly higher rate of pCR than BRCA wild-type patients (56% versus 37%, p=0.04) with neoadjuvant PARPi. There was no difference in pCR when PARPi were combined with carboplatin (+/- chemotherapy) (40% versus 44%, p=0.69). Among RCTs (n=457) patients received PARPi in combination with either Paclitaxel plus Carboplatin (PCb) (85%) or with Paclitaxel alone (P) (15%). PARPi were associated with a higher pCR which approached, but did not meet statistical significance (51% vs 41%; Odds Ratio [OR]: 1.30, 95%CI 0.97 to 1.74, p=0.08). gBRCAm was associated with higher pCR compared to wild type in RCTs analysis (60% versus 48%; OR: 1.64, 95%CI 1.01 to 2.68, p=0.05). The most common adverse events (AEs) were cytopenias, nausea, fatigue, alopecia, and dizziness. Hematological toxicities were the most frequent serious AEs, including anemia (15%), neutropenia (22%), and thrombocytopenia (3%). The combination of PARPi and carboplatin was associated with higher hematological AEs (78% versus 46%; P=0.002). Conclusions: The addition of PARPi in the neoadjuvant setting improves pCR in early-stage HER2-negative breast cancer and germline BRCA 1/2 mutations, but not for unselected patients. Combination of PARPi with carboplatin does not improve pCR and leads to substantially worse toxicity. Further studies are warranted to identify the best neoadjuvant PARPi schema.

*Median. N, number; AC, anthracyclines and cyclophosphamide; mo, months, wks, weeks.