Abstract Prepectoral versus subpectoral implant-based breast reconstruction: A systemic review and meta-analysis. Edvin Ostapenko, MD1,2, Larissa Nixdorf, MD1, Yelena Devyatko, MD1, Ruth Exner, MD1, Kerstin Wimmer, MD1, Florian Fitzal, MD1 1Department of General Surgery and Breast Health Center, Medical University of Vienna, Vienna, Austria. 2Faculty of Medicine, Vilnius University, Vilnius, Lithuania Abstract Background Implant-based breast reconstruction (IBBR) is still standard and most popular option for women undergoing breast reconstruction after mastectomy worldwide. Recently, prepectoral IBBR has resurged in popularity, despite limited data comparing prepectoral with subpectoral IBBR. Methods A systematic search of PubMed and Cochrane Library from January 1, 2011, to December 31, 2021, was performed following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) reporting guideline, data were extracted by independent reviewers. Random and fixed-effect models were applied to obtain pooled proportions and 95% CIs. The Risk of Bias in Nonrandomized Studies- of Interventions (ROBINS-I) tool was used for critical appraisal of cohorts and funnels plots, and the Egger bias test were used for evaluating the publication bias. Studies that compared prepectoral IBBR with subpectoral IBBR for breast cancer were included. Results Overall, 15 studies with 3101 patients were included in this meta-analysis. Our results showed that patients receiving prepectoral IBBR experienced fewer capsular contracture (odds ratio [OR], 0.54; 95% CI, 0.32-0.92; P=.02), animation deformity (OR, 0.02; 95% CI, 0.00-0.25; P=.002), and prosthesis failure (OR, 0.58; 95% CI, 0.42-0.80; P=.001). There was no significant difference between prepectoral and subpectoral IBBR in overall complications (OR, 0.83; 95% CI, 0.64-1.09; P=.19), seroma (OR, 1.21; 95% CI, 0.59-2.51; P=.60), hematoma (OR, 0.76 95% CI, 0.49-1.18; P=.22), infection (OR, 0.87; 95% CI, 0.63-1.20; P=.39), skin flap necrosis (OR, 0.70 95% CI, 0.45-1.08; P=.11), and recurrence (OR, 1.31; 95% CI, 0.52-3.39; P=.55). Similarly, no significant difference was found in Breast-Q scores between prepectoral and subpectoral IBBR groups. Conclusion The results of our systematic review and meta-analysis demonstrated that prepectoral implant-based breast reconstruction is a safe modality and have similar outcomes with significantly lower rates of capsular contracture, prosthesis failure and animation deformity compared to subpectoral implant-based breast reconstruction. Future research should include randomized clinical trials or well-designed prospective matched studies with adequate follow-up to assess long-term as well as oncologic outcomes between comparative groups. Key Words: immediate implant-based breast reconstruction, breast cancer, outcomes, prepectoral, subpectoral; Citation Format: Edvin Ostapenko, Larissa Nixdorf, Yelena Devyatko, Kerstin Wimmer, Ruth Exner, Florian Fitzal. Prepectoral versus subpectoral implant-based breast reconstruction: A systemic 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 P2-15-05.