Real-world incidence, subtype-specific risk, and outcomes of brain metastases (BM) in 2,775 metastatic breast cancer (MBC) patients from the Austrian AGMT_MBC registry, with a median follow-up of 77 months.
17.2% of patients developed BM during the metastatic course. BM risk was highest in HR+/HER2+ (OR 4.43) and HR−/HER2+ (OR 3.57) subtypes vs. luminal MBC; TNBC had OR 2.91. BM were associated with markedly shorter OS (HR 4.23; p<0.001). TNBC had the worst OS after BM diagnosis (4.7 months). Brain-only disease conferred better OS than concurrent extracranial disease (HR 0.58; p=0.001). Focal radiotherapy or neurosurgery outperformed whole brain radiotherapy, which declined over time.
Registry-based design limits causal inference and may have incomplete treatment data. Receptor discordance data (HR loss 14.5%, HER2 gain 9.8%) may reflect biopsy sampling bias. The Austrian single-country cohort may limit generalizability to other healthcare settings.
HER2+ and TNBC patients face the highest BM risk and shortest survival after BM—prioritize active CNS surveillance and enroll these patients in BM-specific trials. When BM are detected, focal radiotherapy or neurosurgery is associated with longer OS than whole brain radiotherapy.
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