Abstract Background: Breast reconstruction (BR) is an essential component of breast cancer treatment, contributes to quality of life. Implant-based techniques are the most commonly used for immediate reconstruction following mastectomy. Subpectoral implant placement offers benefits such as reduced implant palpability and decreased risk of rippling. Complete implant coverage also provides greater protection and prevents lateral migration of the implant. Traditionally, the inferolateral coverage in total submuscular reconstruction is achieved using the serratus anterior muscle flap (SMF). However, this approach is associated with potential donor site morbidity. Alternatives include synthetic meshes, acellular dermal matrices (ADMs), dermal flaps, and the serratus anterior fascia flap (SFF). The high cost limits the widespread use of ADMs. The SFF has emerged as a promising autologous alternative. Despite its potential, limited data exist on the use of SFF in immediate BR. This study aims to compare clinical, surgical and oncologic outcomes, including time to first adjuvant therapy between patients undergoing subpectoral BR with either the SFF or the SMF for inferolateral implant coverage. Methods: A retrospective review was conducted of 209 medical records of women aged 18 years or older diagnosed with stage I-III invasive breast carcinoma. All patients underwent mastectomy followed by immediate subpectoral implant-based BR and received subsequent adjuvant chemotherapy or radiotherapy at Aristides Maltez Hospital, Salvador-BA, Brazil from January 2018 to December 2022. Patients were grouped based on the type of inferolateral implant coverage used: SFF (n=53; 25.4%) or SMF (n=126; 60.3%). Thirty patients with unrecorded flap details were excluded from analysis. Clinical, oncologic, and demographic data were extracted from medical records. The time from surgery to the initiation of adjuvant therapy (defined as either first chemotherapy cycle or first radiotherapy session) was calculated. Results: The median age was 44 years (IQR 38-50), with a predominantly black women population (90.5%). The SFF group received significantly larger implants 375 mL (IQR 305-475) vs. 337.5 mL (IQR 300-390); p=0.01 and had a higher rate of direct-to-implant reconstruction (98.1% vs. 61.2%; p0.01). No significant differences were observed between groups regarding age, menopausal status, clinical stage. The median time from surgery to initiation of adjuvant therapy was 11 weeks in both groups. Conclusions: The SFF is a viable and cost-effective alternative to SMF or ADMs in immediate BR. It supports the use of larger implants, does not delay the initiation of adjuvant therapy. These findings highlight the broader applicability of SFF in reconstructive planning, particularly in resource-constrained settings. Citation Format: L. d. Paz, J. V. Biazús. Serratus anterior fascia flap versus muscle flap for implant coverage in immediate subpectoral breast reconstruction 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 PS2-03-25.
Paz et al. (Tue,) studied this question.