Henry‐Tillman, Ronda

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.

Abstract Introduction: Individuals with cancer may be at higher risk of atrial fibrillation (AF). However, sufficient data are lacking in AF risk among breast cancer survivors, especially for the mid-to long-term risk of AF and the impact of cancer treatment on this association. We aimed to investigate the risk of incident AF in women diagnosed with breast cancer and evaluate the association by length of follow-up and breast cancer treatment. Methods: Using the Korean Health Insurance Service database, we studied 96,476 women who were diagnosed with breast cancer (aged≥20 years) without prior history of AF and breast cancer and underwent breast cancer surgery between January 2007 and December 2013. They were matched 1:3 to a cancer-free population (n=289,428) based on birth year and sex and were followed to the end of 2018. Using ICD-10 codes (I48.0 to I48.4, I.48.9), AF was defined when it was a discharge diagnosis or was verified more than twice in an outpatient clinic. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) of AF associated with breast cancer relative to the cancer-free population, adjusting for age, income, and comorbidities including diabetes, hypertension and hyperlipidemia. Results: During a median follow-up of 6.8 years, AF developed in 2,105 women with breast cancer (3.2 per 1,000 person-years). Mean age at baseline among participants was 49.6 years. Having breast cancer was associated with increased risk of AF (HR, 2.04; 95% CI, 1.93-2.15). This association was stronger for women aged <50 years (HR, 3.98; 95% CI, 3.59-4.40). When we repeated analyses with lag periods of two years to explore the possibility of reverse causation and mid-to long-term risk of AF (n=91,370), the association was largely attenuated but remained significant (HR, 1.18; 95% CI, 1.09-1.28 for total women and HR, 1.60; 95% CI, 1.38-1.86 for women aged <50 years). However, no increased risk of AF was observed in women with breast cancer aged >65 years. Compared with no use of anthracyclines and taxanes, respectively, ever use of anthracyclines and taxanes was associated with increased risk of AF after further adjusting for other cancer treatment modalities including use of trastuzumab, radiotherapy, and endocrine treatment (HR, 1.25; 95% CI, 1.12-1.40 and HR, 1.37; 95% CI, 1.23-1.53, respectively). This association persisted only among women with breast cancer ever treated with anthracyclines when analysis was limited to those with two year-lag periods (HR, 1.23; 95% CI, 1.04-1.45). Conclusions: In this large-scale nationwide cohort study in South Korea, women with breast cancer had an elevated risk of incident AF, especially for women with breast cancer younger than 50 years, regardless of the length of follow-up. Our findings also suggest that cardiotoxic side effects of cancer treatment such as use of anthracyclines might increase both short-term and mid-to long-term risk of AF among women with breast cancer. Citation Format: Yong-Moon ("Mark") Park, Wonyoung Jung, Yohwan Yeo, Sang Hyun Park, Ronda Henry-Tillman, Hong Seok Lee, Tasneem Z. Naqvi, Kyungdo Han, Dong Wook Shin. Risk of atrial fibrillation among women diagnosed with breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3214.