Abstract OT-23-02: Volumetric analysis of the pectoralis major muscle as preoperative tool to select patients undergoing pre-pectoral versus sub-pectoral implant based breast reconstruction after risk reducing mastectomy

Background: Proper patient selection is crucial to maximize aestethic outcome in breast reconstructive surgery. No specific patients selection criteria have been developed to choose between prepectoral versus subpectoral implant-based reconstruction. A quantitative tool able to determine the pectoralis muscle individual characteristics might be helpful to discriminate a priori the patients who will experience better aesthetic outcome and less complications following a pre-pectoral versus a sub-pectoral approach. Preoperative pectoralis muscle assessment may optimize patients’ selection for the breast reconstructive technique. Trial design: This is a multicentric trial in which, patients candidated to risk reducing mastectomy fulfilling inclusion criteria, will undergo a preoperative MRI prior to randomization to pre-pectoral versus sub-pectoral implant placement in immediate breast reconstruction. Volumetric analysis of the pectoralis major muscle (cm2) and measurement of the subcutaneous adipose tissue in the breast region, will be performed to assess anatomic characteristics of the pectoralis muscle using a sagittal T1 fat suppressed sequence. The volume of the pectoralis muscle will be calculated by measuring differences in density with the MRI. In all patients, the pectoralis muscle area on the left and right side will be determined separately and the two values will be averaged. The volumetric assessment will be performed by two expert radiologists. BREAST-Q© questionnaire will be completed by each patient prior to surgery and at the follow up evaluations. Breast reconstruction will be performed immediately after nipple-sparing mastectomy (Arm 1: breast implant placed above the pectoralis major muscle (pre-pectoral); Arm 2: breast implant placed below the pectoralis major muscle (sub-pectoral)). Number of revisional surgeries, explantations, infections, seromas, flap necrosis, will be compared between two groups and correlated with MRI pectoralis muscle volume. Post-operative follow-up evaluations at 6 and 12-months to assess capsular contracture and BREAST-Q changes will be performed. Eligibility criteria: Inclusion criteria: •Female patient•Ages 18-60•Patients undergoing risk reducing mastectomy with immediate implant-based reconstruction •Signed informed consent Exclusion Criteria: •Prior chest wall irradiation •Patients with a contraindication to immediate breast reconstruction.•Patients with history of smoking, •BMI> 40, •D cup breast size•grade III ptosis Aims: To identify variables measured at preoperative MRI pectoralis muscle’s volumetric analysis that correlate with aesthetic outcome and complication rate in pre-pectoral versus sub-pectoral implant based reconstruction. Statistical methods: The assumption of distributional normality will be tested using the Shapiro-Wilk test. Comparisons of two variables will be carried out using the Wilcoxon test for paired groups and the Mann-Whitney test for unpaired groups. Present accrual and target accrual: The trial has been submitted for IRB approval at the ethical commission of Italian Switzerland. Recruitment has not started yet. With an enrollment ratio of 1:1, fifty patients (25 per arm) need to be recruited to ensure a power of 80% with a two sides alpha error of 0.05. Contact information: marialuisa.gasparri@eoc.ch Citation Format: Maria Luisa Gasparri, Thorsten Kuehn, Isabel Rubio, Philip Poortmans, Diana Lueftner, Orit Kaidar-Pearson, Beat Thuerlimann, Yves Harder, Daniel Schmauss, Francesco Meani, Claudia Rauh, Michael David Mueller, Malgorzata Banys-Paluchowski, Andrea Papadia, Valerio Vitale, Stefania Rizzo, Oreste Davide Gentilini. Volumetric analysis of the pectoralis major muscle as preoperative tool to select patients undergoing pre-pectoral versus sub-pectoral implant based breast reconstruction after risk reducing mastectomy [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-23-02.