Cancer incidence in people with intellectual or developmental disability: a matched population-based cohort study in Canada

Global evidence regarding cancer risk among adults with intellectual or developmental disabilities is inconclusive, with mixed evidence and heterogenous methods. We compared cancer incidence rates among Canadian adults with and without intellectual or developmental disabilities. We conducted a matched population-based cohort study in Ontario using administrative health data (1993–2024). Adults with intellectual or developmental disabilities were identified using an algorithm. Adults with intellectual or developmental disabilities were hard matched 4:1 on birth year and sex with non-disabled individuals. We estimate​d incidence rate ratios (IRR) with 95% confidence intervals (CI) comparing adults with and without intellectual or developmental disabilities using generalized estimating equations with a Poisson distribution. For overall cancer, cancer diagnostic groups, and cancer sites, we repor​t IRR with 95% CI overall, by sex, and by age group. 121,080 adults with intellectual or developmental disabilities and 484,320 adults without intellectual or developmental disabilities were included. The incidence rates per 100,000 person years for any cancer were 447.90 (95% CI 439.00–456.98) and 507.36 (95% CI 502.66–512.11) for adults with and without intellectual or developmental disabilities, respectively. While adults with intellectual or developmental disabilities had a lower incidence of cancer than their matched counterparts (IRR = 0.88; 95% CI 0.85–0.90), younger adults with intellectual or developmental disabilities had a higher incidence of cancer compared to individuals without (18–30 years: IRR = 1.43; 95% CI 1.28–1.59; 31–39 years: IRR = 1.54; 95% CI 1.40–1.70). These findings varied by cancer type. Adults with intellectual or developmental disabilities experience an excess of cancer at younger ages compared to non-disabled individuals. This evidence could inform clinical decision-making and policy development, including strategies for improving the accessibility of screening and health promotion.