Assessing the Hazard of Tobacco-Related Cancers Among Individuals With Psychiatric Disorders in British Columbia

Abstract

Individuals with psychiatric disorders (PD) have a high prevalence of tobacco use. However, smoking-cessation treatments are poorly integrated into psychiatric care, and little is known about the tobacco-related (TR) cancer trajectories in these populations. In this study we aim to assess the hazard of developing a TR cancer among individuals with PD. Several population-based provincial databases (Medical Services Plan (MSP), Discharge Abstracts data (DAD) and PharmaNet/PharmaCare) were used to identify individuals in BC diagnosed with depression (n=56,097), schizophrenia (n=2,206), bipolar disorder (n=520), anxiety disorders (n=22,370) or multiple PD (n=42,559) between 1990 and 2013. A primary population-proxy control group (appendicitis) (n=41,537) was also identified using these databases and matched to the psychiatric cohort on age at diagnosis, gender, year of hospital admission and postal code. We linked individuals in the cohort and control group with the BC Cancer Registry. Using a competing-risks approach, we estimated the effect of having a PD on the risk of developing a TR cancer, in light of the competing risk of mortality (with the use of Vital Statistics Deaths database). 165, 288 patients were included in the matched cohort. Individuals with depression (HR=0.81; p<0.01; 95% CI: 0.73-0.91), anxiety disorders (HR=0.84; p=0.02; 95% CI: 0.73-0.97) or multiple PD (HR=0.74; p<0.01; 95% CI: 0.66-0.83) had a statistically significant lower risk of a TR cancer compared to the control group. Individuals with schizophrenia (HR=0.86; p=0.40; 95% CI: 0.62-1.21) or bipolar disorder (HR=0.58; p=0.12; 95% CI: 0.29-1.14), however, showed no statistically significant difference from the control group. Individuals with depression, anxiety disorders or multiple PD diagnoses had a significantly reduced risk of developing a TR cancer. These results were unexpected, and further analyses are required to assess whether clinically less relevant TR cancers are identified in the control group because of a higher engagement in health services, including screening for TR cancers.