The investigators conducted a large, multicenter retrospective study of patients with breast cancer leptomeningeal metastasis (BCLM), constituting one of the largest and most comprehensively curated cohorts to date. Data from 403 patients diagnosed between November 2013 and November 2025 were collected from three major academic centers. Detailed clinical, pathological, diagnostic, and treatment data were analyzed. Overall survival (OS) was evaluated, and independent prognostic factors were identified via Cox regression. A novel Breast Cancer Leptomeningeal Graded Prognostic Assessment (BC-LGPA) model was developed and validated for risk stratification.