Abstract PS5-02-14: "longterm" - long-term response (>18 months) in metastatic her2-positive breast cancer: a retrospective analysis of patients diagnosed between 2010 and 2020 in the german bngo network

Abstract Background Progression-free survival (PFS) and overall survival (OS) have significantly improved in patients with HER2-positive metastatic breast cancer (mBC) due to advances in targeted therapies. The current standard first-line treatment includes dual antibody therapy with trastuzumab and pertuzumab combined with chemotherapy, as established in the CLEOPATRA trial. This real-world data (RWD) analysis, conducted by the German Association of Private Practice-Based and Outpatient Gynecologic Oncologists (BNGO), retrospectively examined patients with a PFS >18 months. Methods This multicenter, retrospective, non-interventional RWD analysis included patients newly diagnosed with HER2-positive metastatic or inoperable breast cancer between January 1, 2010, and July 31, 2019. Data collection occurred between March 1, 2022, and December 31, 2023, using existing site documentation. Data were pseudonymized and entered into standardized electronic case report forms (eCRFs) via a common electronic data capture (EDC) system. Patients were included if they had HER2 IHC 3+ and/or ISH positivity and a PFS of at least 18 months following first-line therapy.Inclusion Criteria- First diagnosis of metastatic or inoperable disease between 01.01.2010 and 31.07.2020- HER2 IHC 3+ and/or ISH-positive at first metastatic diagnosis or in the primary tumor if unknown in metastases- PFS >18 months, assessed clinically or radiologically (RECIST 1.1)- Receipt of anti-HER2 therapy as first-line treatmentExclusion Criteria- No documented HER2+ status in metastases or primary tumor- Disease progression within 18 months of diagnosis Results Of 111 patients from 24 sites, 95 were eligible. Median age at diagnosis was 61.1 years. Of these, 58.9% had prior early-stage HER2+ disease, 33.7% were de novo metastatic, and 7.4% showed HER2 receptor conversion. ER and PR positivity were recorded in 72.6% and 58.9% of patients, respectively. Table 1 summarizes the distribution of metastatic sites at diagnosis.Chemotherapy combined with anti-HER2 therapy was administered in 74.7% of cases, with trastuzumab used in 98.9% and pertuzumab in 66.3%. Endocrine therapy was given in 63.2% of patients, often sequentially. At the end of follow-up, 69.5% of patients remained under therapy, 14.7% had died, and 2.1% were lost to follow-up. Conclusion This RWD analysis provides insight into the evolving treatment patterns and outcomes of long-term responders with HER2-positive metastatic breast cancer. All patients received anti-HER2 therapy, most commonly the trastuzumab-pertuzumab combination. Hormone receptor-positive patients often received sequential endocrine therapy. The findings reflect adherence to international guidelines (ASCO, NCCN, AGO) and highlight the role of national networks such as BNGO in generating meaningful real-world oncology data. Citation Format: G. E. Heinrich. "longterm" - long-term response (>18 months) in metastatic her2-positive breast cancer: a retrospective analysis of patients diagnosed between 2010 and 2020 in the german bngo network [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-02-14.