Risk For Recurrent Stroke In Subjects Newly Diagnosed With Cancer Varies Significantly According To Previous History Of Stroke

Background: Cancer is an important yet understudied risk factor for ischemic stroke. We sought to examine the relationship between previous stroke and risk for future stroke in individuals newly diagnosed with cancer. Methods: Using a provincial administrative database, we conducted a population-based matched cohort study of adults in Ontario, Canada, from 2010-2019. Individuals with a new diagnosis of cancer and a history of ischemic stroke were matched (1:4) by age, sex, year of cancer diagnosis, cancer stage, and cancer site to cancer patients without a history of stroke. The cohort was followed until death, stroke, or March 31, 2020, whichever occurred first. Cumulative incidence function (CIF) curves were created for the incidence of stroke (primary outcome), with the date of cancer diagnosis as the index date. Sub-distribution adjusted hazard ratios (aHR) and 95% confidence intervals (CI) were calculated, where death was treated as a competing event. We further stratified those with a history of stroke by the timing of their most recent stroke: 0-1 years, 1-2 years, 2-5 years, or 5-10 years. Regression analyses were adjusted for baseline characteristics. Results: We examined 65,525 individuals with a new diagnosis of cancer, including 13,105 with a history of ischemic stroke and 52,420 without; the incidence of stroke outcome following cancer diagnosis was 5.5% and 1.8%, respectively. Cancer patients with a history of previous stroke had an increased risk for stroke after cancer diagnosis compared to those without a history of stroke (aHR 2.70 95%CI [2.42-3.00]). Individuals with stroke within the preceding 1 year of the cancer diagnosis had the highest risk of recurrent stroke with aHR 3.64 (95%CI 3.17-4.17). Conclusion: Individuals who have a history of stroke prior to a diagnosis of cancer were more likely to suffer stroke after cancer diagnosis, especially if that stroke had occurred within the year preceding the cancer diagnosis. This finding has potentially important implications for advancing strategies to prevent stroke in patients with cancer.