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

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.