Ten-year temporal distribution of brain metastases after breast cancer: a global cohort study
César Cimonari de Almeida1, Diogo Haddad Santos2, Pedro Lucas Machado Magalhães3
1Division of Neurosurgery, Department of Neurology, University of São Paulo, São Paulo, SP, Brazil.
Purpose:
Brain and central nervous system (CNS) metastases are major contributors to morbidity and mortality in patients with breast cancer (BC). However, their long-term temporal distribution in large real-world populations remains incompletely characterized. This study evaluated the occurrence of brain and CNS metastasis-coded events during the ten years following BC diagnosis using a large federated electronic health record network.
Methods:
A retrospective cohort study was conducted using the TriNetX Global Collaborative Network. Adult patients with BC (ICD-10-CM C50) diagnosed between January 1, 2006, and January 1, 2026, were included if they had no prior or synchronous brain or CNS metastasis. Outcomes were identified using ICD-10-CM codes C79.31, C79.3, and C79.4. Brain and CNS metastasis-coded events were evaluated across consecutive one-year follow-up intervals (0-1 to 9-10 years). Interval-specific event proportions and TriNetX-generated CNS metastasis-free probability estimates were assessed using the number of patients with available follow-up within each interval as the denominator.
Results:
The initial query identified 1,644,204 patients with BC. In the 0-1-year interval analysis, 1,625,953 patients contributed to the assessment. Brain and CNS metastasis-coded events were recorded throughout the follow-up period, with the highest absolute event count occurring during the first year (10,153 events; event proportion 0.6%). The CNS metastasis-free probability estimate at one year was 99.27%. Interval-specific event proportions remained relatively stable across follow-up, ranging from 0.4% to 0.7%. In a separate aggregate analysis, approximately 1.9% of patients had at least one recorded brain or CNS metastasis-coded event during the available follow-up period.
Conclusion:
Brain and CNS metastasis-coded events were observed throughout the ten years following BC diagnosis, with the greatest event burden occurring during the first year after diagnosis and persisting at lower frequencies thereafter. These findings provide a descriptive overview of the temporal distribution of brain and CNS metastasis-coded events in a large real-world cohort. Future studies incorporating molecular subtype information, treatment characteristics, imaging confirmation, and competing-risk methodologies are warranted to further refine risk characterization.
