Abstract PS1-41: Does complete surgical removal of metastases in oligometastatic breast cancer improve survival? A matched-pair analysis of the AGMT_MBC-registry
Authors: Gampenrieder Simon Peter , Rinnerthaler Gabriel , Tinchon Christoph , Petzer Andreas Leo , Suppan Christoph , Heibl Sonja , Voskova Daniela , Zabernigg August F , Egle Daniel , Sandholzer Margit , Singer Christian F , Roitner Florian , Andel Johannes , Hubalek Michael , Knauer Michael , Greil Richard 
Published: February 2021

Abstract
Background: Metastatic breast cancer (MBC) is generally thought to be a systemic and incurable disease requiring systemic therapy. However, surgical resection of oligometastatic disease might be of benefit similar to other malignant diseases. Here, we present the results from a matched analysis of patients undergoing radical surgery of metastases.
Methods: The MBC registry of the Austrian Study Group for Medical Tumor Therapy (AGMT) is an ongoing multicenter registry for MBC patients in Austria. Patients undergoing surgical removal of all metastatic sites (+/- primary tumor and lymph node dissection) were identified and matched 1:1 according to disease-free survival (de novo metastatic vs. &lt; 24 vs. ≥ 24 months), location of metastases, subtype (HR+/HER2- vs. HR+/HER2+ vs. HR-/HER2+ vs. triple-negative) and age (≥ 60 vs. &lt; 60). OS was defined as time from diagnosis of metastatic disease until death. Only patients with available matching parameters and sufficient outcome data were included in this analysis.
Results: As of 24/06/2020, 1904 patients were enrolled into the AGMT_MBC-Registry; 24 of them received surgery of metastases and 23 had a complete match with patients without surgery. In the surgery group, five patients (21.7%) received immediate postperative chemotherapy and 80.0% received further chemotherapy after surgery. Out of patients with HR+ disease (n=15), 86.7% received endocrine therapy prior and/or after surgery. We found a numerically but not statistically significant longer overall OS in patients undergoing surgery (47.4 vs. 29.6 months, HR 0.61; 95%CI 0.30-1.24; P=0.171). Two, five and ten year survival estimates were 82.6% (95%CI 68.5-99.6), 31.3% (95%CI 15.7-62.5) and 31.3% (95%CI 15.7-62.5) in the surgery group and 59.1% (95%CI 41.7-83.7), 24.8% (95%CI 11.7-52.6) and 13.2% (95%CI 4.0-43.1) in the non-surgery group, respectively. The largest benefit for surgery was found in the luminal and HER2-positive subtypes, while no benefit was observed in the triple-negative subgroup.
Conclusion: Radical surgery of all metastases seems to improve survival, especially in luminal and HER2-positive subtypes, however, the analysis did not reach statistical significance, most probably due to the low patient number. Furthermore, because of the retrospective and non-randomized design, a systematic bias cannot be totally excluded.
Citation Format: Simon Peter Gampenrieder, Gabriel Rinnerthaler, Christoph Tinchon, Andreas Leo Petzer, Christoph Suppan, MD, Sonja Heibl, Daniela Voskova, August F Zabernigg, MD, Daniel Egle, MD, Margit Sandholzer, MD, Christian F Singer, Florian Roitner, Johannes Andel, Michael Hubalek, Michael Knauer, Richard Greil. Does complete surgical removal of metastases in oligometastatic breast cancer improve survival? A matched-pair analysis of the AGMT_MBC-registry [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 PS1-41.