MMDA-19 ISOLATED BRAIN METASTASES VERSUS BRAIN PLUS EXTRACRANIAL METASTASES IN DE NOVO METASTATIC BREAST CANCER: MOLECULAR SUBTYPE-SPECIFIC SURVIVAL OUTCOMES AND TREATMENT PATTERNS FROM THE SEER DATABASE (2010–2022)
Pragya JainAbstract
Background
Brain metastases (BM) are a devastating complication of metastatic breast cancer (MBC), with limited data comparing isolated BM versus BM with concurrent extracranial metastases (ECM) across molecular subtypes. We investigated survival outcomes and treatment patterns of isolated versus non-isolated BM in de novo stage IV breast cancer by molecular subtype.
Methods
Using SEER 17 (2010–2022), we identified de novo MBC patients with known BM status classified by subtype (HR+/HER2−, HR+/HER2+, HR−/HER2+, TNBC) and metastatic pattern: isolated BM (no concurrent bone, liver, or lung metastases) versus BM with ECM. Kaplan-Meier and log-rank tests compared overall survival (OS). Chi-square tests assessed treatment differences.
Results
Among 36,853 de novo MBC patients, 2,703 (7.3%) had BM at diagnosis; 2,358 had known subtypes. Of these, 417 (17.7%) had isolated BM and 1,941 (82.3%) had BM with ECM. The isolated BM cohort was enriched for TNBC (30.9% vs. 19.8%, p < 0.001) with higher surgical rates (25.4% vs. 9.5%, p < 0.001). Overall, isolated BM patients had superior OS (mOS 13 vs. 11 months, p = 0.0005). The survival benefit was subtype-dependent. HR−/HER2+ patients showed the most striking differential: mOS 29 vs 11 months, 2-year OS 57.4% vs. 28.9% (p = 0.0002). TNBC patients with isolated BM also benefited (mOS 8 vs. 6 months, p = 0.0009), while no difference was seen in HR+/HER2− disease (p = 0.10). Among isolated BM patients, surgery (mOS 23 vs. 10 months, p = 0.0001), radiation (mOS 17 vs. 6 months, p < 0.0001), and chemotherapy (mOS 22 vs 4 months, p < 0.0001) each improved survival. Increasing extracranial burden showed stepwise decrement: 0 sites (13 months), 1 (14), 2 (11), 3 (7 months).
Conclusions
Isolated BM in de novo MBC represent a distinct entity with subtype-specific prognostic implications. HR−/HER2+ patients with isolated BM demonstrate a nearly 3-fold survival advantage over those with concurrent ECM, supporting subtype-stratified treatment and aggressive multimodal intervention.