Abstract PS1-01-21: Smaller implant volume compared to native breast volume increases capsular contracture risk

Abstract Purpose: This study aimed to identify clinical, surgical, and treatment-related predictors of capsular contracture (CC) following immediate implant-based breast reconstruction after mastectomy, with particular emphasis on the influence of implant size relative to resected breast volume. Methods: We conducted a retrospective review of 465 patients who underwent nipple- or skin-sparing mastectomy and immediate reconstruction (direct-to-implant or two-stage) between 2004 and 2020. CC was defined as Baker grade II or higher. Capsular contracture-free interval (CCFI) was measured from final implant placement to first documented CC. Univariable and multivariable logistic regression identified CC risk factors. CCFI was assessed by Kaplan-Meier analysis and Cox proportional-hazards modeling. The optimal implant-to-breast weight ratio cut-point was determined using maximally selected rank statistics (surv_cutpoint). Results: Over a median follow-up of 63.7 months, 50 of 465 patients (10.8%) developed CC. In multivariable logistic regression, subpectoral placement (OR 3.28; 95% CI 1.05-10.21; P = 0.041) and postmastectomy radiotherapy (PMRT) (OR 4.94; 95% CI 2.27-10.74; P < 0.001) remained independent predictors of CC, whereas implant undersizing < 80% did not reach significance (OR 2.14; 95% CI 0.90-5.10; P = 0.085). In time-to-event analysis, PMRT alone independently shortened the capsular contracture-free interval (CCFI) (HR 4.04; 95% CI 2.11-7.74; P < 0.001). A maximally selected cut-point of 69.1% implant-to-breast ratio optimally stratified CC risk: patients with ratios ≤ 69.1% had significantly lower 1- and 5-year CCFI (84.2% and 75.8% vs. 96.5% and 90.3%; log-rank P < 0.001) and a threefold increased CC hazard in both unadjusted (HR 3.25; 95% CI 1.63-6.50; P < 0.001) and adjusted Cox models (HR 3.02; 95% CI 1.47-6.21; P = 0.003). Conclusion: Implant undersizing, particularly implant volumes ≤ 69.1% of resected breast volume, together with subpectoral placement and PMRT, are independent risk factors for capsular contracture. Careful matching of implant size to native breast volume may reduce CC risk in immediate reconstruction. Citation Format: H. Koh, K. Yoon, H. Shin, E. Kim. Smaller implant volume compared to native breast volume increases capsular contracture risk [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 PS1-01-21.