Cancer morbidity and mortality in individuals with obsessive-compulsive disorder: a population-based and sibling cohort study in Sweden and Denmark

Abstract Background Assessing the risk of cancer morbidity and mortality in individuals with obsessive-compulsive disorder (OCD) is important to identify potential disparities in cancer incidence and prognosis. In this study, we aimed to assess the overall and site-specific cancer risk among individuals with OCD, as well as their cancer-specific and all-cause mortality following a cancer diagnosis. Methods This cohort study used population-based matched cohorts and sibling-matched cohorts from Sweden (people born between 1932 and 2010) and Denmark (1932–2009). OCD diagnoses were derived by the Swedish National Patient Register and the Danish Psychiatric Central Register. Each individual with OCD was matched with 20 individuals without OCD on sex, birth year, and calendar time and, in separate analyses, with their OCD-free full siblings. Follow-up began at the index date (OCD diagnosis or matching date) and continued until an incident cancer diagnosis, death, emigration, or end of follow-up (December 31, 2016, in Sweden, or 2015, in Denmark). To assess mortality risk in the Swedish population-matched cohort, individuals diagnosed with cancer were subsequently followed from cancer diagnosis until death, emigration, or end of follow-up. Results In the population-based matched cohorts, 1,372 (2.4%) of 57,239 individuals with OCD and 30,376 (2.7%) of 1,144,780 unaffected individuals developed cancer. OCD was not associated with overall cancer risk (pooled HR 0.99, 95% CI 0.94–1.04). In Sweden, OCD was associated with a lower risk of prostate cancer (HR 0.79, 95% CI 0.65–0.97) and melanoma (HR 0.67, 95% CI 0.51–0.89). Following a cancer diagnosis, individuals with OCD showed no clear difference in cancer-specific mortality (HR 1.10, 95% CI 0.97–1.25), but showed higher all-cause mortality (HR 1.27, 95% CI 1.14–1.42), compared with individuals without OCD. Conclusions OCD was not associated with overall cancer risk or cancer-specific mortality. However, it was associated with a higher risk of all-cause mortality after cancer diagnosis. There does not seem to be a higher-than-expected cancer burden in this population. However, the higher all-cause mortality after a cancer diagnosis suggests that clinical attention should be directed toward managing comorbid conditions to bridge the mortality gap.