Investigating inequalities in cancer staging and survival for adults with intellectual or developmental disabilities and cancer: A population-based study in Manitoba, Canada

Background: Cancer is a leading cause of death among adults living with intellectual or developmental disabilities (IDD). However, few epidemiological studies exist worldwide quantifying inequalities in cancer stage at diagnosis and survival for people with IDD relative to those without IDD.

Methods: A population-based, retrospective cohort study was conducted using provincial health and social administrative data in Manitoba, Canada. Adults (≥18 years) with a cancer diagnosis between 2004 and 2017 were included. Lifetime IDD was identified before the cancer diagnosis using an established algorithm. Modified Poisson regression with robust error variance was used to estimate the association between IDD status and metastatic cancer at diagnosis. Multivariable Cox proportional hazards analyses were used to the effect of IDD on overall survival following the cancer diagnosis.

Results: The staging and prognosis cohorts included 62,886 (n = 473 with IDD) and 74,143 (n = 592 with IDD) cancer patients, respectively. People living with IDD were significantly more likely to be diagnosed with metastatic cancer and die following their cancer diagnosis compared to those without IDD (RR=1.20; 95 % CI 1.05-1.38; HR= 1.53; 95 % CI 1.38-1.71). Significant heterogeneity by sex was identified for cancer survival (p = 0.005).

Discussion: People with IDD had more advanced cancer stage at diagnosis and worse survival relative to those without IDD. Identifying and developing strategies to address the factors responsible that contribute to these disparities is required for improving patient-centred cancer care for adults with IDD.