Abstract PS12-21: First-line treatment of hormone receptor positive metastatic breast cancer (MBC) in everyday practice: Results from the Austrian AGMT_MBC-Registry
Authors: Rinnerthaler Gabriel , Gampenrieder Simon P , 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

Background: International guidelines recommend endocrine-based first-line therapy [ET] in hormone receptor-positive, HER2-negative (HR+/HER2- or luminal) metastatic breast cancer (MBC), nowadays in combination with a CDK4/6 inhibitor. Several real-word data suggest, however, that in daily practice up to 40% of patients with luminal MBC receive chemotherapy in first-line. To clarify the treatment landscape in an Austrian population of HR+/HER2- MBC patients, we analyzed the data from the MBC registry of the Austrian Study Group for Medical Tumor Therapy (AGMT-MBC-Registry). In addition, we investigated the influence of different treatment strategies on overall survival (OS). Methods: The AGMT-MBC-Registry is an ongoing multicenter registry for MBC patients in Austria. Only patients with HR+/HER2- MBC with available ER and HER2 status and sufficient outcome data were included in this analysis. Unadjusted, univariate survival probabilities of PFS and OS were calculated by the Kaplan-Meier method and compared by the log-rank test, multivariate hazard ratios (HR) were estimated by Cox regression models. A multivariate analysis including the following parameters was performed for first-line PFS and OS: age (continuous, as interaction with menopausal status), menopausal status (pre- vs postmenopausal vs unknown,), DFS (de novometastatic vs &lt; 24 months vs ≥ 24 months), (neo)adjuvant chemotherapy (yes vs no), grading (1+2 vs 3 vs unknown), visceral disease (yes vs no) and number of metastatic sites (1 vs 2-3 vs ≥4), first-line treatment (ET+CDK4/6i vs ET vs chemotherapy +/- bevacizumab +/- ET). Results: As of 24/06/2020, 1904 patients were included in the AGMT-MBC-Registry. Out of 1633 evaluable patients, 931 (57.01%) had HR+/HER2- disease and had received at least one treatment line for metastatic disease. In first-line, 577 (62.0%) patients received endocrine-based therapy (356 [61.7%] ET, 172 [29.8%] ET+CDK4/6i, 49 [8.5%] ET+Targeted other), and 354 (38.0%) received chemotherapy. The proportion of chemotherapy treated patients was slightly higher in pre- vs. postmenopausal women (41/94=43.6% vs. 222/664=33.4%) but decreased significantly over time (&lt;2010: 60.3%; 2010-2015: 44.8%; &gt;2015: 19.7%). In multivariate analysis, both ET and ET+CDK4/6i were significantly associated with longer first-line PFS and OS compared to chemotherapy (Table 1).

The most frequently used drugs across all treatment-lines were aromatase inhibitors (77.9%), fulvestrant (53.9%; 39.8% in first-line and 36.3% in second-line), tamoxifen (17.2%), CDK4/6 inhibitors (40.0%; 48.9% in first-line and 21.8% in second-line), everolimus (18.9%; 30.7% in second-line and 69.3% in ≥ third-line), taxanes (41.6%), capecitabine (35.0%), anthracyclines (28.6%), vinorelbine (17.0%) and eribulin (12.6%). Conclusion: In our registry, first-line chemotherapy for luminal MBC was significantly associated with an inferior PFS and OS compared to endocrine-based therapy. Because of the retrospective design of the study, biases influencing these results cannot be fully excluded, however, our data suggest that first-line chemotherapy should be avoided in luminal MBC.

Adjusted analysisET vs. chemotherapyET+CDK4/6i vs. chemotherapy1st-line PFSHR 0.63; 95%CI 0.52-0.77; P&lt;0.001HR 0.19; 95%CI 0.13-0.29; P&lt;0.001OSHR 0.59; 95%CI 0.49-0.72; P&lt;0.001HR 0.35; 95%CI 0.23-0.51, P&lt;0.001

Citation Format: Gabriel Rinnerthaler, Simon P Gampenrieder, Christoph Tinchon, Andreas Leo Petzer, Christoph Suppan, Sonja Heibl, Daniela Voskova, August F Zabernigg, Daniel Egle, Margit Sandholzer, Christian F Singer, Florian Roitner, Johannes Andel, Michael Hubalek, Michael Knauer, Richard Greil. First-line treatment of hormone receptor positive metastatic breast cancer (MBC) in everyday practice: Results from the Austrian 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 PS12-21.