Neither Hormonal Factors Nor AGEs Explain Lower Prostate Cancer Risk in Older Men With Diabetes Mellitus

CONTEXT: Diabetes mellitus is conventionally associated with an increased risk of cancer; however, inverse associations of diabetes with prostate cancer are well described. Mechanisms are unclear, although hormonal factors, including alterations in sex hormone and IGF1 concentrations due to metabolic disturbances, have been hypothesized to play a role. OBJECTIVE: To assess sex hormones, IGF1, glucose, and advanced glycation end products (AGEs) as potential mediators of the association between diabetes mellitus and prostate cancer. DESIGN AND PARTICIPANTS: Longitudinal cohort study. The association of baseline diabetes with prostate cancer incidence was assessed using proportional hazards competing risks analysis in 3149 men followed for 12 years. Baseline hormone, glucose, and carboxymethyllysine (CML) levels were examined as potential mediators of this association. RESULTS: Diabetes was associated with a lower prostate cancer risk (fully adjusted subhazard ratio, 0.63; 95% CI, 0.43 to 0.92; P = 0.017). This association was unchanged after accounting for testosterone, DHT, estradiol, or SHBG. Similarly, the addition of IGF1 or its binding proteins 1 and 3, or glucose, did not alter this association. CML was not associated with the risk of prostate cancer, and additional correction for CML in the fully adjusted model did not alter the inverse association of diabetes and prostate cancer risk. CONCLUSIONS: In this study, alterations in sex hormone, IGF1, glucose, and CML levels did not account for the inverse association of diabetes and prostate cancer risk. Further studies are required to provide more insight into underlying causes of this association.