This study evaluated the influence of prognostic factors and whole brain radiotherapy (WBRT) on overall survival (OS) of breast cancer (BC) patients with brain metastases (BM).

Medical records of 730 BC patients diagnosed with BM from 2000 to 2014 at 17 institutions were retrospectively reviewed. OS was calculated from BM diagnosis. Median follow-up duration was 11.9 months (range, 0.1–126.2).

Median OS was 15.0 months (95% CI: 14.0–16.9). Patients with different BC-specific graded prognostic assessment (GPA) scores showed significant differences (p < 0.001) in OS. In multivariate analysis, histologic grade 3 (p = 0.014), presence of extracranial metastasis (p < 0.001), the number of BM (>4; p = 0.002), hormone receptor negativity (p = 0.005), HER2-negativity (p = 0.003), and shorter time interval (<30 months) between BC and BM diagnosis (p = 0.007) were associated with inferior OS. By summing the β-coefficients of variables that were prognostic in multivariate analyses, we developed a prognostic model that stratified patients into low-risk (≤0.673) and high-risk (>0.673) subgroups; the high-risk subgroup had poorer median OS (10.1 months, 95% CI: 7.9–11.9 vs. 21.9 months, 95% CI: 19.5–27.1, p < 0.001). Univariate and multivariate analyses of propensity score-matched patients diagnosed with BM ≥ 30 months after BC diagnosis (n = 389, “late BM”) revealed that WBRT-treated patients showed superior OS compared to non-WBRT-treated patients (p = 0.070 and 0.030, respectively).

Our prognostic model identified high-risk BC patients with BM who might benefit from increased surveillance; if validated, our model could guide treatment selection for such patients. Patients with late BM might benefit from WBRT as initial local treatment.