Abstract Background: Although the Japanese Breast Cancer Clinical Practice Guideline (2022) allow immediate breast reconstruction (IBR) after neoadjuvant chemotherapy (NAC) with caution, concerns remain regarding delayed would healing, increased surgical complications, and unknown oncologic safety. We aimed to evaluate the safety and oncologic outcomes of IBR following NAC by comparing patients with and without NAC at our institution. Methods: We retrospectively reviewed 228 breast reconstructions performed at the time of mastectomy from July 2013 to September 2024. Of these, 29 breasts (13.0%) underwent IBR after NAC (NAC group), and 194 breasts (87.0%) were reconstructed without NAC (control group). We analyzed clinicopathological characteristics, operative time, blood loss, length of hospital stay, postoperative complications, recurrence, and survival. Median follow-up was 73 months (range, 3-134). Results: Patient age and surgical procedures (including nipple-sparing mastectomy rates: 41.4% vs 44.3%) were comparable. Autologous reconstruction was more frequent in the control group (27.3% vs 10.3%, p=0.06). No significant differences were observed in: operative time: 254 vs 271.5 min (p=0.71), blood loss: 65 vs 63 mL (p=0.71), hospital stay: 13 vs 14 days (p=0.26), overall complication rate: 37.9% (NAC) vs 30.4% (control) (p=0.42), major complications requiring reoperation: 13.3% vs 13.0% (p=1.00). Local recurrence occurred in 1 (3.4%) vs 7 (3.6%) cases (p=1.00). Distant recurrence was significantly more common in the NAC group (17.2% vs 0.52%, p=0.0005), as was breast cancer-specific mortality (10.3% vs 0%, p=0.002). These outcomes likely reflect the higher baseline recurrence risk of the NAC group. Conclusions: Immediate breast reconstruction following NAC was not associated with increased surgical risk. Although oncologic outcomes were worse in the NAC group, this is likely attributable to patient selection with inherently higher recurrence risk. With proper patient counseling and risk stratification, IBR after NAC can be considered a safe and feasible option. Further prospective studies incorporating patient-reported outcomes are warranted. Citation Format: M. Tomiguchi, K. Hidaka, L. Goto-Yamaguchi, Y. Yamamoto. Safety and Oncologic Outcomes of Immediate Breast Reconstruction Following Neoadjuvant Chemotherapy abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-05-06.
Tomiguchi et al. (Tue,) studied this question.