Associations of Diabetes, Smoking, and Metabolic Factors With the Risk of Breast and Prostate Cancers: A Population‐Based Retrospective Cohort Study

BACKGROUND: Previous studies reported an inverse association between diabetes and prostate cancer. Moreover, the associations of smoking with breast and prostate cancers remain inconclusive. This study aims to investigate whether diabetes, smoking, or metabolic factors are associated with female breast and prostate cancers incidence, and explore factors associated with their prevalence. METHODS: In this retrospective cohort study, patients who utilized public healthcare services between year 2000 and 2021 in Hong Kong were identified. For cancer incidence, patients (n = 192,456) were followed up until a diagnosis of cancer. Factors associated with site-specific cancer incidence were assessed using Cox regression, whereas factors associated with site-specific cancer prevalence were examined using logistic regression. RESULTS: Patients with diabetes did not have a higher risk of developing breast (adjusted hazard ratio [aHR]: 1.11, 95% CI = 0.86-1.42) or prostate cancer (aHR: 0.94, 95% CI = 0.72-1.21) when compared to those without diabetes. The associations with breast cancer remained consistent when stratified by menopausal status. Smoking was associated with an increased risk of prostate cancer (aHR: 1.16, 95% CI = 1.04-1.30) but not for breast cancer. However, male patients who had diabetes, elevated lipid levels, haematuria, or cystitis were more likely to have a previous prostate cancer diagnosis. CONCLUSION: Findings indicate no significant association between diabetes and incidence of breast or prostate cancer, but suggest smoking as a potential risk factor for prostate cancer.