ESTRO 2024 - Abstract Book

S560

Clinical - Breast

ESTRO 2024

Alexander Fabian 1 , Daniel Buergy 2 , Nora Amirpour-Mehrhof 3 , Denise Bernhardt 4 , Alicia S Bicu 2 , Konstantinos Ferentinos 5 , Eleni Gkika 6 , Hossein Hemmatazad 7 , Katharina Hintelmann 8 , Juliane Hörner-Rieber 9 , Stefan Janssen 10,11 , Heiko Karle 12 , David Kaul 3 , Tim Lange 13 , Montserrat Pazos 14 , Susanne Rogers 15 , Eugenia Vlaskou Badra 16 , Fabian Weykamp 9 , Thomas Brunner 17 , Andrea Wittig 18 , Marciana Nona-Duma 19 , Oliver Blanck 1 , David Krug 1 1 University Hospital Schleswig-Holstein Campus Kiel, Department of Radiation Oncology, Kiel, Germany. 2 University Medical Center Mannheim, University of Heidelberg, Department of Radiation Oncology, Mannheim, Germany. 3 Charité — Universitätsmedizin Berlin, Department of Radiation Oncology, Berlin, Germany. 4 Technical University of Munich, Department of Radiation Oncology, Munich, Germany. 5 German Oncology Center, European University of Cyprus, Department of Radiation Oncology, Limassol, Cyprus. 6 University Medical Center Freiburg, Department of Radiation Oncology, Freiburg, Germany. 7 Inselspital, Bern University Hospital, University of Bern, Department of Radiation Oncology, Bern, Switzerland. 8 University Medical Center Hamburg-Eppendorf, Department of Radiotherapy and Radiation Oncology, Hamburg, Germany. 9 University Hospital Heidelberg, Department of Radiation Oncology, Heidelberg, Germany. 10 University of Lubeck, Department of Radiation Oncology, Lubeck, Germany. 11 Medical Practice for Radiotherapy and Radiation Oncology, Department of Radiotherapy and Radiation Oncology, Hannover, Germany. 12 University Medical Center of the Johannes Gutenberg-University Mainz, Department of Radiotherapy and Radiation Oncology, Mainz, Germany. 13 Hannover Medical School, Clinic for Radiotherapy, Hannover, Germany. 14 University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany. 15 Kantonsspital Aarau, Radiation Oncology Center KSA-KSB, Aarau, Germany. 16 University Hospital & University of Zurich, Department of Radiation Oncology, Zurich, Switzerland. 17 University Hospital Graz, Department of Radiation Oncology, Graz, Germany. 18 University Hospital Würzburg, Department of Radiation Oncology, Würzburg, Germany. 19 HELIOS Hospital Schwerin, Department of Radiation Oncology, Schwerin, Germany

Purpose/Objective:

Metastasis-directed therapy (MDT) has been shown to improve progression-free (PFS) and overall survival (OS) in the primary tumor-agnostic SABR-COMET-trial for patients with oligometastatic disease. However, in the phase II NRG-BR002 and EXTEND-trials, MDT failed to improve PFS in oligometastatic breast cancer patients. Several single arm trials established the local efficacy of stereotactic radiotherapy (SRT) in the treatment of intra- and extracranial breast cancer metastases. However, little is known about the effect of metastatic site, tumor subtype and prior treatment on outcomes including local recurrence (LR), PFS, or OS after SRT. The purpose of this report is to describe cohort characteristics and to investigate effects of metastatic site on outcomes after SRT.

Material/Methods:

We conducted a retrospective multicenter cohort study of MDT in patients with breast cancer among 14 member institutions of the interdisciplinary DEGRO working group Radiosurgery and Stereotactic Radiotherapy. Patients were eligible for analysis if they had metastatic breast cancer and received MDT using SRT to a biologically equivalent dose ( / β=10 Gy) of at least 45 Gy delivered over a maximum of 12 treatment sessions. Analyses were exploratory. A cumulative incidence function was used to estimate LR rates which were compared between groups using Gray's test. PFS and OS were compared using the log-rank test. Outcomes were computed using the interval between the first course of treatment until LR, progression or death. Patients were stratified into those with intra- and extracranial metastases.