Background Recognition of new risk factors for cancer could reveal new interventions in the prevention of one of the world’s leading causes of morbidity and mortality. It has been hypothesised that depression is associated with an increased risk of cancer but evidence remains inconclusive. This study aims to examine the association between various measures of depression and cancer incidence at several sites.

Methods Data from an existing cohort of UK adults (the Health and Lifestyle Survey, 1984/5) was linked to follow up data from cancer registries to form a study population of 8,446 individuals with no history of cancer. A past history of severe depression was self-reported at baseline. Psychological distress was assessed using the 30-item version of the General Health Questionnaire (GHQ) and six depression questions in the GHQ produced a depression score. Cox proportional hazards models were used to estimate the risk of overall cancer and separately for lung, colorectal, breast and prostate cancer, among those with a history of severe depression, psychological distress and depressive symptoms.

Results During a mean follow-up of 19.3 years, 986 people obtained at least one cancer registration. A history of severe depression was associated with a 23% increased risk of overall cancer (95% CI 1.05–1.43) and a 53% increased risk of lung cancer (95% CI 1.07–2.2) but this became non-significant following adjustment for confounders. After adjustment, a significant positive association remained between depression scores and prostate cancer and a between depression scores and overall cancer incidence in men. However, these results are likely to have occurred by chance due to the large number of tests performed.

Conclusion Overall there was no compelling evidence that there is a causal relationship between depression and cancer. This, combined with other evidence, can be used to address concerns of cancer patients with regards to what caused their cancer.