The purpose of this multicenter retrospective cohort study is to determine the effect of radiotherapy on capsular contraction and implant loss rates in patients undergoing prepectoral immediate implant-based breast reconstruction (IBBR) comparing Polyurethan (PU) and non-PU covered implants.

Breast cancer affects 2.6 million women worldwide annually, with surgery as the standard treatment for 95% of cases. Rising mastectomy rates, due to advanced diagnostic tools and patient preferences, make immediate breast reconstruction crucial for improving quality of life for around 650,000 women each year. Prepectoral implant-based breast reconstruction (IBBR) has become a preferred approach due to advancements like synthetic meshes, acellular dermal matrices (ADM), and polyurethane (PU) covered implants, which show promise in reducing complications such as capsular contracture, implant loss, and breast animation deformities. Radiotherapy (RT), however, increases these risks, especially for capsular contracture, underscoring the need for strategies to mitigate such outcomes.

This multicenter retrospective cohort study will investigate the impact of radiotherapy on complications such as capsular contracture and implant loss in patients with breast cancer who underwent mastectomy and prepectoral IBBR. The study will compare outcomes between PU and non-PU covered implants using data from approximately 30 international sites. Patient information will be extracted from hospital records, coded for confidentiality, and analyzed statistically to achieve the study's objectives of improving post-reconstruction outcomes and quality of life for patients.

Inclusion Criteria:

• Patients with signed General consent or study specific consent form
• Patients with confirmed diagnosis of primary or recurrent breast cancer
• Patients undergoing nipple - or skin-sparing mastectomy with prepectoral IBBR (all types of implants, with or without mesh, all types of biologic and synthetic mesh, one- or two- stage) in the setting of PMRT (or any type or RT before reconstruction) between 2016 and 2022.
• Patients undergoing two-stage IBBR with radiotherapy to the expander before reconstruction with implant.
• Patients with recurrent breast cancer after breast conserving surgery and radiotherapy.
• Follow up must be at least 2 years after IBBR.
• Patients aged 18 and above will be eligible for inclusion.

Exclusion Criteria:

• Patients who have explicitly refused the further use of their data through a consent declaration.
• Patients undergoing subpectoral IBBR or autologous reconstruction as initial type of reconstruction.
• No radiotherapy.

data will be collected from patient hospital records, including approximately 30 international sites