Cancer survival in the context of mental illness: a national cohort study

Abstract

Objective: To explore the reasons for worse cancer survival in people with experience of mental illness, including differences by cancer type and psychiatric diagnosis.

Method: New Zealand breast and colorectal cancer registrations (2006-2010) were linked to psychiatric hospitalization records for adults (18-64 years). Cancer-specific survival was compared for recent psychiatric service users and nonusers using Cox regression. The contributions of deprivation, comorbidity and stage at diagnosis were assessed for those with schizophrenia or bipolar affective disorder (Group A) and others using mental health services (Group B).

Results: Of 8762 and 4022 people with breast and colorectal cancer respectively, 440 (breast) and 190 (colorectal) had recent contact with psychiatric services. After adjusting for confounding, risk of death from breast cancer was increased for Group A [Hazard Ratio (HR) 2.55 (95% confidence interval 1.49-4.35)] and B [HR 1.62 (1.09-2.39)] and from colorectal cancer for Group A [HR 2.92 (1.75-4.87)]. Later stage at diagnosis contributed to survival differences for Group A, and comorbidity contributed for both groups. Fully adjusted HR estimates were breast: Group A 1.65 (0.96-2.84), B 1.41 (0.95-2.09); colorectal: Group A 1.89 (1.12-3.17), B 1.25 (0.89-1.75)].

Conclusions: The high burden of physical disease and delayed cancer diagnosis in those with psychotic disorders contributes to worse cancer survival in New Zealand psychiatric service users.

Keywords: Breast neoplasms; Colorectal neoplasms; Healthcare disparities; Mental disorders; Schizophrenia.