Relative Incidence and Mortality Rates of Common Cancers in People with Severe Mental Illness in UK Primary Care

Abstract

Background: The relationship between severe mental illnesses (SMI) and cancer is complex and previous study findings are inconsistent. We aimed to investigate the relationship between SMI and cancer incidence and mortality in a national cohort with the largest SMI patient population to date. Methods: In this UK-wide cohort study using primary care records we calculated incidence and mortality rates of all-cancer, and bowel, lung, breast or prostate cancer, in patients with SMI, compared to matched patients without SMI. We used competing risks regression to account for mortality from other causes. Outcomes: 69,632 patients had an SMI diagnosis. The rate of all-cancer diagnoses was reduced in those with SMI (Hazard ratio (HR):0·95; 95%CI 0·93-0·98) and particularly in those with schizophrenia (HR:0·82; 95%CI 0·77-0·88) compared to those without SMI. Cancer diagnosis rate remained lower in patients with schizophrenia when accounting for the competing risk of premature mortality. All-cause mortality after cancer diagnosis was increased in the SMI group, and cancer-specific mortality was increased in those with schizophrenia (HR: 1·96; 95%CI 1·57-2·44). Interpretation: Patients with schizophrenia have lower rates of cancer diagnosis than patients without SMI. However, once diagnosed, SMI patients have higher mortality rates and those with schizophrenia have higher cancer-specific mortality. These findings likely reflect barriers to cancer diagnosis and treatment in SMI, which need to be identified and addressed. Funding Statement: This study was supported by Public Health England, Wellcome Trust, Medical Research Council, University College London Hospitals NIHR Biomedical Research Centre and the NIHR ARC North Thames Academy. Declaration of Interests: We declare no competing interests. Ethics Approval Statement: Ethical approval for this study was obtained from the Independent Scientific Advisory Committee of CPRD (protocol no. 18_288). Informed consent was waived because data are anonymized for research purposes.