Project Summary/Abstract One in eight women will develop breast cancer in her lifetime, causing both physical and psychological trauma due to invasive treatments and the distress associated with removal of a breast. Breast reconstruction after mastectomy has become a critical procedure for many women to restore psychological wellbeing, with implant-based reconstruction the most common approach. Nearly 100,000 patients undergo reconstruction with implants every year in the United States. Surgical mesh devices, particularly acellular dermal matrices, are now used off-label by most reconstructive surgeons performing prosthetic breast reconstruction. In the past decade, surgeons have advocated a transition from submuscular reconstruction (placement of the implant under the pectoralis muscle) to pre-pectoral (placement above the pectoralis) and often consider mesh to be necessary for this procedure. Surgical mesh has not been approved by the FDA for breast reconstruction for either anatomic location. These mesh devices, similar to vaginal mesh, are considered Class III medical devices and FDA recently prioritized the evaluation of these products during a panel meeting in 2019. No Level I randomized trial has been successfully performed to determine the actual risks and benefits of mesh devices in breast reconstruction. Although the existing data are primarily retrospective and observational, multiple small studies and meta-analyses on submuscular reconstructions have found increased complication rates with the use of surgical mesh and no benefit in patient satisfaction. Practice trends have deviated from this conclusion, largely related to the low quality of the existing studies. As surgeons transition to the pre-pectoral plane, mesh manufacturers have concluded that it is impossible to perform a Level I study due to a perceived paucity of surgeons who would perform pre-pectoral reconstruction without their mesh assistance. Nonetheless, several plastic surgeons have questioned this assumption and are supportive of a randomized study, especially because mesh has been associated with higher complications in prior studies in the submuscular plane, and is an expensive burden on the healthcare system (up to 20,000 dollars per breast depending on the product). It is now critical and feasible to rigorously evaluate these implanted mesh devices that are being used, off-label, in vulnerable breast cancer patients. This study proposes the first ever randomized, multi-center trial for mesh assistance in two-stage prosthetic pre-pectoral breast reconstruction, across the major manufacturers. Importantly, it will be the first study to include a control cohort that does not receive mesh and will comply with FDA regulations including an approved Investigational Device Exemption. The goals are to demonstrate feasibility of such a study and to generate high level data toward the evaluation of safety and effectiveness of these products for the benefit of women’s pub...