Introduction: Small observational studies with short-term follow-up suggest that cancer patients are at reduced risk of Alzheimer’s disease (AD) compared to the general population.
Methods: A nationwide cohort study using Danish population-based health registries (1980-2013) with cancer patients (n = 949,309) to identify incident diagnoses of AD. We computed absolute reductions in risk attributed to cancer and standardized incidence rate ratios (SIRs) accounting for survival time, comparing the observed to expected number of AD cases.
Results: During up to 34 years of follow-up of cancer survivors, the attributable risk reduction was 1.3 per 10,000 person-years, SIR = 0.94 (95% confidence interval 0.92-0.96). SIRs were similar after stratification by sex, age, and cancer stage, and approached that of the general population for those surviving >10 years.
Discussion: Inverse associations between cancer and AD were small and diminished over time. Incidence rates in cancer survivors approached those of the general population, suggesting limited association between cancer and AD risk.
Keywords: Alzheimer’s disease; dementia; epidemiology; neoplasms; risk.