Risk of Cancer Following an Ischemic Stroke in the Canadian Longitudinal Study on Aging

ABSTRACT: Background: Stroke survivors may be at higher risk of incident cancer, although the magnitude and the period at risk remain unclear. We conducted a retrospective cohort study to compare the risk of cancer in stroke survivors to that of the general population. Methods: The Canadian Longitudinal Study on Aging is a large population-based cohort of individuals aged 45–85 years when recruited (2011–2015). We used data from the comprehensive subgroup (n = 30,097) to build a retrospective cohort with individual exact matching for age (1:4 ratio). We used Cox proportional hazards models to estimate hazard ratios of new cancer diagnosis with and without a prior stroke. Results: We respectively included 920 and 3,680 individuals in the stroke and non-stroke groups. We observed a higher incidence of cancer in the first year after stroke that declined afterward (p-value = 0.030). The hazard of new cancer diagnosis after stroke was significantly increased (hazard ratio: 2.36; 95% CI: 1.21, 4.61; p-value = 0.012) as compared to age-matched non-stroke participants after adjustments. The most frequent primary cancers in the first year after stroke were prostate (n = 8, 57.1%) and melanoma (n = 2, 14.3%). Conclusions: The hazard of new cancer diagnosis in the first year after an ischemic stroke is about 2.4 times higher as compared to age-matched individuals without stroke after adjustments. Surveillance bias may explain a portion of post-stroke cancer diagnoses although a selection bias of healthier participants likely led to an underestimation of post-stroke cancer risk. Prospective studies are needed to confirm the potentially pressing need to screen for post-stroke cancer.