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Background: Neoadjuvant systemic therapy is increasingly applied in breast cancer patients to improve surgical and oncological outcomes. There is only limited data from clinical practice on the relevance of body mass index (BMI) on the pathologic complete response (pCR) rate following neoadjuvant systemic treatment (NST). We aimed to retrospectively analyze the impact of BMI on pCR after NST for Dutch breast cancer patients. Methods: Patients diagnosed with invasive breast cancer between 2019 and 2021 who were treated with NST followed by a surgical procedure, were selected from the Netherlands Cancer Registry (NCR). Patients were divided into three groups based on BMI: patients with underweight/normal weight (BMI< 25 kg/m2), patients with overweight (BMI 25-29.9 kg/m2) and patients with obesity (BMI>30 kg/m2). Patients with unknown BMI, ER/PR/HER2 or pCR status were excluded for analysis. The primary outcome was pCR after NST. The association between BMI and pCR was estimated using logistic regression models with the expression of odds ratios (ORs). Results: After applying in- and exclusion criteria, 4430 patients were included for analysis, statified into four molecular breast cancer subtypes; HR+/HER2- (n=2256), HR+/HER2- (n=722), HR-/HER2+ (n=405) and HR-/HER2- (n=1047). The predictors age, differentiation grade, histological type, clinical tumor (cT) and nodal (cN) stage and molecular breast cancer subtype were found siginificant for achieving pCR after NST. Multivariabele regression analysis identified differentiation grade, cT and cN stage and molecular subtype as independent predictors for pCR after NST. There was no association between pCR and (continuous or categorical) BMI. Above mentioned analyses performed by stratification according to molecular breast cancer subtype, also showed no statistically meaningful association between BMI and pCR. Conclusion: In this nationwide retrospective cohort study, evaluating 3340 patients with invasive breast cancer, we found no evidence of BMI being a predictive factor for achieving pCR following NST in neither the whole cohort, nor stratified according to molecular breast cancer subtype. Table 1. Multivariable regression analysis of the total cohort Citation Format: Britt Jansen, Anke Gielen, Mariette Agteroff, Marissa van Maaren, Sandra Beijer, Martine Moossdorff, Marjolein Smidt, Emily Postma. PD12-07 The effect of BMI on the pathological response after neoadjuvant systemic therapy in breast cancer patients: a nationwide retrospective study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD12-07.

Objective To describe a suitable alternative technique for reconstruction of the pelvic floor after extensive resection. To review our outcomes of gluteal VY plasty in the reconstruction of the pelvic floor after extensive abdominoperineal resection (conventional or extralevator abdominoperineal resection, total pelvic exenteration, or salvage surgery). Design Retrospective cohort study. Setting An academic hospital and tertiary referral centre for the treatment of locally advanced or locally recurrent rectal cancer, and salvage surgery in The Netherlands. Patients Forty-one consecutive patients who underwent a pelvic floor reconstruction with gluteal VY plasty at Maastricht University Medical Centre between January 2017 and February 2021 were included. The minimum duration of follow-up was 2 years. Main outcome measures Perineal herniation is the primary outcome measure. Furthermore, the occurrence of minor and major postoperative complications and long-term outcomes were retrospectively assessed. Results Thirty-five patients (85.4%) developed one or more complications of whom twenty-one patients experienced minor complications and fourteen patients developed major complications. Fifty-seven percent of complications was not related to the VY reconstruction. Six patients (14.6%) recovered without any postoperative complications during follow-up. Three patients developed a perineal hernia. Conclusions A gluteal VY plasty is a suitable technique for reconstruction of the pelvic floor after extensive perineal resections resulting in a low perineal hernia rate, albeit the complication rate remains high in this challenging group of patients.

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