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Background: Approximately 5% of breast cancer patients carry a deleterious germline BRCA1/2 mutation, which leads malignant cells to be deficient in the repair of DNA double-strand breaks via homologous recombination. The poly(adenosine diphosphate–ribose) polymerase (PARP) enzymes are important on DNA single-strand break repair and PARP inhibitors (PARPi) cause an accumulation of unresolved DNA damage in tumors with BRCA1/2 mutations, resulting in cell death. However, because platinum salts also ultimately cause double-strand DNA breaks and may have overlapping mechanisms of resistance with PARPi, the efficacy of PARPi in patients with prior platinum therapy is unknown. We sought to evaluate the efficacy of PARPi in patients with BRCA1/2-related breast cancer and previous platinum exposure. Methods: We performed a systematic review and meta-analysis of studies that evaluated the efficacy of PARPi in patients with advanced or metastatic breast cancer and germline BRCA1/2 mutations. Two independent investigators identified double-blind, randomized controlled trials (RCTs) that included the subgroup of previous exposure to platinum. PubMed, Embase, and Cochrane databases were searched for papers up to June 26, 2022. Data extraction from published reports and quality assessment were performed under Cochrane recommendations. Hazard ratios (HRs) with a 95% confidence interval (CI) were pooled, and a p-value of < 0.05 was considered statistically significant. The software Review Manager 5.3 was selected for conducting the statistical analysis. The primary endpoint of interest was progression-free survival (PFS). Results: Out of 2069 database results (487 on PubMed; 1376 on Embase; and 206 on Cochrane), 42 studies were selected for full review, and 4 RCTs, with a total of 249 patients, were included in the final investigation. The PARPi included were Olaparib, Talazoparib, Niraparib, and Veliparib. Pooled analysis showed that PARPi improved PFS in breast cancer patients with prior treatment with platinum-based therapy compared to the control group [HR = 0.72; 95% CI, 0.53-0.97; p = 0.03]. In comparison, the population without previous platinum exposure had a similar but slightly greater benefit from PARPi [HR = 0.68; 95% CI, 0.52-0.89; p = 0.005]. A subgroup analysis containing only the three randomized trials with PARPi monotherapy confirmed the central tendency favoring PARPi over physicians’ choice of single-agent chemotherapy in patients with prior platinum-therapy; however, because of small numbers and wide confidence interval it was not statistically significant [HR = 0.72; 95% CI, 0.51-1.01; p = 0.06]. Conclusions: Our findings suggest that PARPi are associated with longer PFS in patients with advanced breast cancer and previous exposure to platinum therapy, decreasing the concerns about cross-resistance between the drug classes. Nonetheless, more extensive studies are still necessary to investigate the efficacy of PARPi in patients with prior platinum exposure and truly platinum-resistant disease. Progression-free survival of included studies Citation Format: Alice D. Marinho, Beatriz Mella S. Pessoa, Gabriela R. Brandao, Caroliny H. Da Silva, Pedro A. Reis, Ana Carolina M. Comini, Felipe Batalini. Efficacy of PARP Inhibitors in Patients With BRCA1/2-related Breast Cancer with Prior Platinum Exposure: A Systematic Review and Meta-Analysis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-08.