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Thesis Format

Integrated Article

Degree

Master of Science

Program

Epidemiology and Biostatistics

Supervisor

Anderson, Kelly K

Abstract

Evidence on cancer incidence in people with psychotic disorders, compared to the general population, is equivocal, although those with psychotic disorders so have more advanced stage of cancer at the time of diagnosis. The objective of this thesis was to compare cancer incidence and stage at diagnosis for people with psychotic disorders, relative to the general population. Our systematic review did not observe a significant difference in overall cancer incidence among people diagnosed with psychotic disorders (RR = 1.08, 95% CI: 1.00 to 1.16), however people with psychotic disorders were more likely to be present with advanced stage cancer at diagnosis (OR = 1.22, 95% CI: 1.02 to 1.46). Our cohort study found an elevated incidence of cancer in people with non-affective psychotic disorder, relative to the general population (IRR = 1.09, 95%CI: 1.05 to 1.12). Significant heterogeneity was found by cancer site. We found significant effect modification by sex, which was removed when we excluded prostate cancer. Additionally, we identified higher odds of more advanced stage at diagnosis in people with psychotic disorders (OR = 1.23, 95% CI: 1.13, 1.34). These findings are indicative of a significant diagnostic delay and a need to increase education and targeted access to care. Future research should examine the confounding effects of lifestyle factors and anti-psychotic medication, as well as potentially intermediary effects of cardiometabolic disorders.

Summary for Lay Audience

It is unclear whether there is a higher incidence of cancer among people with psychotic disorders, as many studies have been published which have found the incidence to be higher or lower than the general population. There is evidence that people with psychotic disorders are more likely to have more advanced stage cancer at diagnosis; however, this evidence is limited by shortcomings and inconsistencies in the methodology of studies conducted on this topic. Although there have been studies on stage at diagnosis and mortality from cancer in Canada, there have been no Canadian studies to date which examine the incidence of cancer among people with psychotic disorders. The provincial health administrative data under Canada’s universal healthcare system provided an opportunity to answer these questions using large, population-based data. Our objectives were to 1) examine the incidence of cancer in people with psychotic disorders and 2) compare the stage of cancer at diagnosis in people with psychotic disorders to that of the general population. Our systematic review did not find a difference in cancer incidence for people diagnosed with psychotic disorders, however people with psychotic disorders were more likely to have a more advanced stage cancer at the time they were diagnosed. Our cohort study found that people with non-affective psychotic disorders had a higher incidence of cancer compared to the general population. We also found that the incidence of certain cancers was higher and lower in people with non-affective psychotic disorders. There was a difference in the incidence of cancer among males with psychotic disorders relative to females with psychotic disorders. This difference was removed when we exclude prostate cancer from our analyses, suggesting that prostate cancer accounts for this difference that had been noted in previous studies. The differences found by cancer site are likely the product of different levels of exposure to risk factors for developing cancer among people with non-affective psychotic disorders, including smoking, cardiometabolic disorders, antipsychotic medication, and screening behaviour. Additionally, we found that people with non-affective psychotic disorders were more likely to have a higher stage at the time they were diagnosed with cancer. This indicates a delay in the diagnosis of cancer in people with non-affective psychotic disorders. Furthermore, we found that people with non-affective psychotic disorders were more likely to have missing data on stage at diagnosis. We recommend that future studies examine the role of risk factors such as smoking, cardiometabolic disorders, and antipsychotic medication in the risk of cancer among people with psychotic disorders. It is also recommended that we implement programs which target cancer education, screening, and early diagnosis among people with psychotic disorders, which may translate into more favourable health outcomes.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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