Background: Whether human insulin can increase the risk of prostate cancer is rarely studied. Patients and Methods: The reimbursement databases of all Taiwanese patients with diabetes from 1996 to 2009 were retrieved from the National Health Insurance databases of Taiwan. An entry date was set at January 1, 2004 and a total of 498,407 men with type 2 diabetes were followed for prostate cancer incidence until the end of 2009. Incidence for ever-users, never-users, and subgroups of human insulin exposure (using tertile cutoffs of time since starting insulin, cumulative dose, and cumulative duration of insulin) were calculated, and the age-adjusted and multivariable-adjusted hazard ratios were estimated using Cox regression. Results: There were 72,948 ever-users and 425,459 never-users, with respective numbers of incident prostate cancer of 768 (1.05%) and 6282 (1.48%), and respective incidence of 236.87 and 276.88 per 100,000 person-years. The overall hazard ratios (95% confidence intervals) indicated a significant negative association with insulin in the age-adjusted model (0.910; 0.843-0.981), but lack of association in the full model adjusted for multivariables (0.989; 0.912-1.072). The hazard ratios for the different categories of the dose-responsive parameters might show significantly lower risk with insulin use in the age-adjusted models, but none of the hazard ratios were significant in the full models. Conclusion: This study suggests a lack of association between the use of human insulin and prostatic cancer risk in patients with type 2 diabetes after multivariable adjustment.
