Abstract P2-14-08: Trends in neoadjuvant systemic therapy rates in Europe: Pre-planned substudy of TAXIS (OPBC-03, SAKK 23/16, IBCSG 57-18, ABCSG-53, GBG 101)

Abstract Introduction: Even though randomized controlled trials could not show a significant survival benefit for the use of neoadjuvant systemic therapy (NST), it is increasingly recommended for patients with clinically node-positive breast cancer due to its implications on prognosis, locoregional downstaging and response-driven adjuvant systemic therapy. The aim of this study was to assess the need for international standardization of treatment recommendations by evaluating clinical practice heterogeneity in use of NST for patients with clinically node-positive breast cancer in Europe. Methods: The study was preplanned in the international multicenter phase-III OPBC-03/TAXIS trial (ClinicalTrials.gov Identifier: NCT03513614) after randomization of the first 500 patients with clinically node-positive breast cancer who underwent axillary lymph node dissection (ALND) or axillary radiation (ART) without ALND after tailored axillary surgery (TAS) in the context of extended regional nodal irradiation. Clinically node-positive breast cancer was defined by confirmed nodal disease at the time of initial diagnosis; in case of neoadjuvant therapy, residual nodal disease was mandatory. Investigators were encouraged to enroll all eligible patients consecutively. However, TAXIS is unique inasmuch as its pragmatic design allows both the neoadjuvant and adjuvant setting according to the preferences of the treating physicians and institutions and thus provides an excellent opportunity to study patterns and trends in use of NST in patients with clinically positive nodes in Europe. Results: A total of 500 patients with a median age of 57 years (IQR: 48-69 years) were included at 44 breast centers in 6 European countries from August 2018 to June 2022. Subtype was hormone receptor (HR) positive (+) and human epidermal growth factor receptor 2 (HER2) negative (-) in 393 (80.0%), HR+/HER2+ in 52 (10.6%), HR-/HER2+ in 5 (1.0%) and HR-/HER2- in 34 (6.9%) patients. The rate of patients undergoing NST was 31.4% with a significant upward trend over time during the study period (from 20.0% in 2018 to 38.1% in 2022; p=0.044). The use of NST varied significantly by country (p=< 0.001) and by site (p=0.015). For patients with clinical AJCC tumor stage II and III, the rates of patients undergoing NST in Switzerland were 26.5% (18 of 68) and 35.9% (92 of 256), in Germany 22.2% (2 of 9) and 30.4% (7 of 23), in Austria 50% (7 of 14) and 60% (9 of 15) and in Hungary 0% (0 of 15) and 20.7% (18 of 87), respectively (p=0.019 and 0.004). Large differences by country were found for ER+/HER2- breast cancer, ranging from 13.1% (11 of 84) in Hungary to 47.8% (11 of 23) in Austria (p=0.007). Within Switzerland, which was the country with most included patients (328 of 500) and participating sites (n=25), the rate of patients undergoing NST for ER+/HER2- breast cancer varied considerably by site, ranging from 10% (2 of 20) to 50% (11 of 22). Discussion: This study revealed substantial heterogeneity in clinical practice in Europe, indicating the need for development of and adherence to consistent guidelines to standardize the international use of NST. Citation Format: Walter P. Weber, Zoltan Matrai, Stefanie Hayoz, Guido Henke, Daniel R. Zwahlen, Günther Gruber, Frank Zimmermann, Thomas Ruhstaller, Simone Muenst, Markus Ackerknecht, Christian Kurzeder, Sherko Küemmel, Vesna Bjelic-Radisic, Viktor Smanykó, Conny Vrieling, Rok Satler, Inna Meyer, Charles Becciolini, Susanne Bucher, Colin Simonson, Peter M. Fehr, Natalie Gabriel, Robert Maráz, Dimitri Sarlos, Konstantin J. Dedes, Cornelia Leo, Gilles Berclaz, Hisham Fansa, Christopher Hager, Klaus Reisenberger, Ákos Sávolt, Christian F. Singer, Roland Reitsamer, Jelena Winkler, Giang Thanh Lam Lam, Mathias K. Fehr, Tatiana Naydina, Magdalena Kohlik, Karine Clerc, Valerijus Ostapenko, Florian Fitzal, Martin Heidinger, Nadia Maggi, Alexandra Schulz, Pagona Markellou, Loïc Lelièvre, Daniel Egle, Jörg Heil, Michael Knauer, Christoph Tausch. Trends in neoadjuvant systemic therapy rates in Europe: Pre-planned substudy of TAXIS (OPBC-03, SAKK 23/16, IBCSG 57-18, ABCSG-53, GBG 101) [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 P2-14-08.