Stage IV breast, colorectal, and lung cancer at diagnosis in adults living with intellectual or developmental disabilities: a population-based cross-sectional study

Background — Cancer is a leading cause of death among people living with intellectual or developmental disabilities (IDD). Although studies have documented lower cancer screening rates, there is limited epidemiological evidence quantifying potential diagnostic delays. This study explores the risk of metastatic cancer stage for people with IDD compared to those without IDD among breast (female), colorectal, and lung cancer patients in Canada.

Methods — Separate population-based cross-sectional studies were conducted in Ontario and Manitoba by linking routinely collected data. Breast (female), colorectal, and lung cancer patients were included (Manitoba: 2004–2017; Ontario: 2007–2019). IDD status was identified using established administrative algorithms. Modified Poisson regression with robust error variance models estimated associations between IDD status and the likelihood of being diagnosed with metastatic cancer. Adjusted relative risks were pooled between provinces using random-effects meta-analyses. Potential effect modification was considered.

Results — The final cohorts included 115,456, 89,815, and 101,811 breast (female), colorectal, and lung cancer patients, respectively. Breast (female) and colorectal cancer patients with IDD were 1.60 and 1.44 times more likely to have metastatic cancer (stage IV) at diagnosis compared to those without IDD (relative risk [RR], 1.60; 95% confidence interval [CI], 1.16–2.20; RR, 1.44; 95% CI, 1.24–1.67). This increased risk was not observed in lung cancer. Significant effect modification was not observed.

Conclusions — People with IDD were more likely to have stage IV breast and colorectal cancer identified at diagnosis compared to those without IDD. Identifying factors and processes contributing to stage disparities such as lower screening rates and developing strategies to address diagnostic delays is critical.