Depression and cancer risk: a register-based study of patients hospitalized with affective disorders, Denmark, 1969-1993

The authors investigated the cancer risk of patients hospitalized for depression in a nationwide Danish cohort study. All 89,491 adults in Denmark who had been admitted to a hospital with depression, as defined in the International Classification of Diseases, Eighth Revision, between 1969 and 1993 were identified. There were 1,117,006 person-years of follow-up. Incidence rates of all cancers and of site-specific cancers were compared with national incidence rates for first primary cancers, with data being adjusted for sex, age, and calendar time. A total of 9,922 cases of cancer were diagnosed in the cohort, with 9,434.6 having been expected; this yielded a standardized incidence ratio of 1.05 (95% confidence interval (CI): 1.03, 1.07). The risk of cancer was increased for the first year after hospital admission, with brain cancer especially occurring more frequently than expected. When the first year of follow-up was excluded, the increase was attributable mainly to an increased risk of tobacco-related cancers: Standardized incidence ratios for non-tobacco-related cancers were 1.00 (95% CI: 0.97, 1.03) after 1-9 years of follow-up and 0.99 (95% CI: 0.95, 1.02) after 10 or more years of follow-up. These data provide no support for the hypothesis that depression independently increases risk of cancer, but they emphasize the deleterious effect that depression can have on lifestyle factors.