Supplemental Material For: Real-World Biomarker Testing and Treatment Patterns in HR+/HER2− Metastatic Breast Cancer: Insights from the AGO QS-Mamma Registry 2024

Data were derived from the AGO QS-Mamma registry 2024, collecting a nationwide, representative sample of real-world breast cancer care in Germany. Patients with HR+/HER2− MBC receiving systemic therapy were included in the analysis. Associations between clinical variables and biomarker testing were assessed using chi-square tests, Cochran–Mantel–Haenszel analysis, and multivariable logistic regression. <br><br>Results: A total of 805 patients with HR+/HER2− MBC were analyzed.

ESR1 testing was performed in 53% of patients in second-line or later. Testing rates increased with prior endocrine therapy exposure (57% after ≥12 months CDK4/6 inhibitor therapy vs. 14% with endocrine therapy alone; p < 0.001). In multivariable analysis, prior endocrine therapy was strongly associated with ESR1 testing (OR 6.20, 95% CI 2.85–13.46 for ≥12 months exposure), whereas treatment line was not.PI3K testing was performed in 15% of patients.

Although higher testing rates were observed in endocrine-resistant patients, this association was not significant after adjustment (p = 0.248), while treatment line was strongly associated with testing (p < 0.001).BRCA testing was performed in 27% of patients and was significantly associated with treatment line (p < 0.001), peaking in second line.<br><br>Conclusion: Biomarker testing in HR+/HER2− MBC reveals heterogeneous implementation in real-world practice.

ESR1 testing is primarily driven by prior endocrine therapy exposure, whereas PI3K and BRCA testing are more strongly influenced by treatment line. These findings highlight gaps in the consistent application of biomarker-guided strategies and underscore the need for improved implementation of testing recommendations – especially given the advancement in available treatment options.</p>