Associations between mental illness and cancer: a systematic review and meta-analysis of observational studies

Considering the impact of mental illness and cancer on the society, the relationship between the two diseases should be assessed. This study aimed at determining the association between mental illness and cancer.

The Embase and Medline databases were searched on October 21, 2020. Cohort, case-control, and cross-sectional studies were eligible for study inclusion. The Newcastle-Ottawa scale was used to qualitatively assess the risk of bias. Funnel plots were drawn to evaluate the risks of bias across the included studies.

We included 58 studies from 16 countries, incorporating approximately 30 national databases and 25 million individuals. Patients with psychiatric disorders did not show an increased risk of developing cancer. However, patients with cancer had a significantly increased risk of developing mental illness. The survival rates of patients with mental illness according to cancer occurrence and patients with cancer according to mental illness occurrence were significantly decreased.

Clinicians should conduct early screening to ensure that appropriate interventions for mental illness are administered in patients with cancer. Due to the high incidence of death in patients with mental illnesses due to unnatural causes, such as suicide, homicide, and accidents, clinicians should be aware of the importance of the treatment and management of these patients.