Abstract PO1-05-13: Drop-out rates from line to line of treatment in metastatic breast cancer (MBC): Results from the Austrian AGMT_MBC-Registry

Abstract Background: In metastatic breast cancer (MBC) continuous treatment with sequentially administered cancer drugs is the standard of care. Lines of treatment (LoT) consisting of single drugs or drug combinations are usually administered until disease progression or unacceptable toxicity. To provide as many patients as possible access to the most effective therapies, the “best treatment first” strategy has been established as a subset of patients will be lost from LoT to LoT. To investigate drop-out rates in all subsequent LoT, high-quality real-world data are needed. Here, we present data from the Austrian Study Group of Medical Tumor Therapy (AGMT) MBC-Registry, a multicenter nationwide ongoing retrospective and prospective registry for MBC patients in Austria. Patients and methods: Patients with known hormone-receptor (HR) and HER2 status, available survival data and at least one LoT were included. Therapies administered between diagnosis or disease progression and subsequent disease progression were counted as one LoT. All types of antitumor drugs (endocrine therapy, targeted therapy, chemotherapy, immunotherapy) were considered. Results: As of 16-May-2023, 2,484 patients were included in the registry. Out of 2,044 evaluable patients, 1,330 (65.1%) were HR+/HER2-, 251 (12.3%) were HR+/HER2+, 146 (7.1%) were HR-/HER2+ and 317 (15.5%) were triple-negative, respectively. The median number of treatment-lines in the overall cohort was 3 (range 1-14; 95%CI 3-3). In patients with HR+/HER2-, HR+/HER2+, HR-/HER2+ and triple-negative tumors the median LoT were 3 (range 1-14; 95%CI 3-4), 4 (range 1-13; 95%CI 3-4), 3 (range 1-10; 95%CI 3-4) and 2 (range 1-9; 95%CI 2-3), respectively. Overall, 641 patients were still on treatment at data cut off. The estimated percentage of patients being treated in each LoT and the corresponding drop-out rates from 1st- to 5th-line are provided in Table 1. Conclusion: Relevant drop-out rates even in the early treatment lines support a “best treatment first” strategy. An accelerated investigation of promising cancer drugs in early treatment lines in patients with MBC is warranted. Drop-out-Rate 1st-line 2nd-line 3rd-line 4th-line 5th-line All n 2044 1281 869 558 344 Drop-out-Rate / 23.8% 24.8% 30.9% 34.0% HR+/HER2- n 1,330 854 586 380 244 Drop-out-Rate / 19.6% 23.0% 29.6% 30.7% HR+/HER2+ n 251 157 109 72 48 Drop-out-Rate / 23.4% 20.4% 25.0% 28.4% HR-/HER2+ n 146 78 59 37 24 Drop-out-Rate / 36.6% 16.9% 36.2% 33.3% Triple-negative n 317 192 115 69 28 Drop-out-Rate / 34.0% 38.2% 39.5% 57.6% Citation Format: Simon Gampenrieder, Gabriel Rinnerthaler, Angelika Pichler, Walter Herz, Andreas Petzer, Clemens Dormann, Marija Balic, Christoph Suppan, Sonja Heibl, Lukas Scagnetti, Margit Sandholzer, Clemens Schmitt, August Zabernigg, Daniel Egle, Petra Pichler, Christopher Hager, Florian Roitner, Johannes Andel, Kathrin Strasser-Weippl, Rupert Bartsch, Michael Hubalek, Michael Knauer, Christian F. Singer, Richard Greil. Drop-out rates from line to line of treatment in metastatic breast cancer (MBC): Results from the Austrian AGMT_MBC-Registry [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-05-13.