Mental disorders, participation, and trajectories in the Danish colorectal cancer screening programme: a population-based cohort study

People with mental disorders exhibit increased mortality due to colorectal cancer, despite having a similar incidence to the general population. We aimed to evaluate the extent to which people with mental disorders participate in organised colorectal cancer screening.We conducted a population-based cohort study of all Danish residents aged 50-74 years who were invited to undergo biennial faecal immunochemical testing between March 1, 2014, and Sept 30, 2018. We used national registry data from all first-time invitees. The primary endpoint was participation within 90 days of invitation. We calculated the proportion who participated and assessed their screening results and adherence to and completeness of follow-up colonoscopy according to their history of mental disorders, classified as none, mild or moderate, or severe. We computed crude and adjusted participation differences in percentage points and participation ratios using the pseudo-observations method.Of 2 036 704 people who were invited, we included 2 036 352 in the final cohort, of whom 1 008 045 (49·5%) were men and 1 028 307 (50·5%) were women, with a mean age of 60·7 years (SD 8·3, range 49-78). Data on ethnicity were not collected. Compared with people with no mental disorders, the adjusted analysis showed lower participation among people with mild or moderate mental disorders (men: participation difference -4·4 percentage points [95% CI -4·7 to -4·1]; women: -3·8 percentage points [-4·1 to -3·6]) and severe mental disorders (men: participation difference -13·8 percentage points [-14·3 to -13·3]; women: -15·4 percentage points [-15·8 to -14·9]). People with mental disorders had a higher proportion of positive faecal immunochemical test results, lower adherence to colonoscopy, and more incomplete colonoscopies than people without mental disorders.People with mental disorders were less likely to participate in colorectal cancer screening than those without these disorders. Patients with mental disorders could benefit from support or encouragement from their general practitioner or mental health-care facility to participate in cancer screening. Potential interventions should consider type of mental disorder, as needs might differ.Danish Cancer Society, Danish Health Foundation.