Abstract 4344364: Time-dependent association between breast cancer and risk of ischemic stroke: a nationwide cohort study

BACKGROUND: The association between breast cancer diagnosis, treatment, and the risk of incident ischemic stroke remains unclear. We aimed to investigate ischemic stroke risk among breast cancer survivors and evaluate the association by age, follow-up duration, and cancer treatments. METHODS: Using the Korean National Health Insurance Service database, we studied 113,232 women newly diagnosed with breast cancer (aged ≥18 years) without prior stroke history who underwent breast cancer surgery between January 2010 and December 2016. Each was matched 1:3 by birth year to a cancer-free female population (n=322,818). Subdistribution hazard ratios (sHRs) and 95% confidence intervals (CIs) were estimated, accounting for death as a competing risk and adjusting for sociodemographic factors and cardiovascular and noncardiovascular comorbidities. RESULTS: Over a mean follow-up of 7.2 years, ischemic stroke occurred in 1,155 (1.0%) breast cancer surgery survivors. Overall, breast cancer survivors had a slightly lower risk of stroke than cancer-free women (sHR 0.94; 95% CI 0.88–1.00). However, stroke risk was elevated in the short term following diagnosis (sHR 1.59, 95% CI 1.34–1.89 at 1 year; sHR 1.17, 95% CI 1.05–1.30 at 3 years) across all age groups, with stronger associations observed at 3 and 6 months post-diagnosis. A reduced risk was observed after 1 year in a landmark analysis that included only individuals event-free at the 1-year follow-up (sHR 0.87, 95% CI 0.81–0.93). Among breast cancer survivors, treatment with anthracycline (sHR 1.25) and the combination of tamoxifen and aromatase inhibitors (sHR 1.49) were associated with increased stroke risk, whereas radiation therapy was associated with decreased risk (sHR 0.84). These associations weakened and became nonsignificant after 1 year. Stroke risk was also higher in breast cancer survivors with low income, hypertension, diabetes, or current smoking. CONCLUSION: The association between breast cancer and ischemic stroke risk is time-dependent, with increased short-term risk post-diagnosis and treatment, followed by a decline over time. These findings highlight the importance of proactive stroke risk management, including baseline cardiovascular assessments and ongoing monitoring for thromboembolic events.