OC-02 - Risk of arterial thromboembolism in patients with breast cancer

Breast cancer is the most common cancer in women and clearly increases the risk of venous thromboembolism. However, its association with arterial thromboembolism is less well defined.

To determine the short-term cumulative incidence and relative hazard of arterial thromboembolism in elderly patients with incident breast cancer.

Using the Surveillance Epidemiology and End Results-Medicare linked database, which includes approximately 28% of all patients diagnosed with cancer in the United States, we identified patients with a new primary diagnosis of breast cancer from 2002 through 2011. These patients were individually matched by age, sex, race, registry, and medical comorbidities to a group of Medicare enrollees without cancer, and each pair was followed through 2012. Validated diagnosis codes were used to identify a primary composite outcome of arterial thromboembolism defined as any ischemic stroke or myocardial infarction. Secondary outcomes included ischemic stroke alone and myocardial infarction alone. Cumulative incidence rates were calculated using competing risk survival statistics. The Gray test was used to compare rates between groups. The proportional hazard assumption was violated for the entirety of patient follow-up; therefore, Cox proportional hazard analysis was performed at discrete time points when the assumption was generally met.

We identified 96,666 pairs of breast cancer patients and matched controls. Median age was 75 years and few cancers were advanced at diagnosis (12% stages 3/4). The 3-month cumulative incidence of arterial thromboembolism was 2.1% (95% confidence interval [CI] 2.0-2.2%) in cancer patients compared to 1.4% (95% CI 1.3-1.5%) in controls (hazard ratio [HR] 1.5, 95% CI 1.4-1.6, p<0.01). The short-term risk of each secondary outcome was heightened in the breast cancer group, although the relative hazard for myocardial infarction was higher than for ischemic stroke. The 3-month cumulative incidence of ischemic stroke was 1.3% (95% CI 1.2-1.4%) in cancer patients compared to 1.0% (95% CI 0.9-1.1%) in controls (HR 1.3, 95% CI 1.2-1.4, p<0.01), and the 3-month cumulative incidence of myocardial infarction was 0.9% (95% CI 0.8-0.9%) in cancer patients compared to 0.4% (0.4-0.5%) in controls (HR 2.0, 95% CI 1.8-2.3, p<0.01). Excess risks attenuated over time and were no longer present beyond 1 year.

Patients with incident breast cancer face an increased short-term risk of ischemic stroke and myocardial infarction.