Diabetes mellitus and prostate cancer risk.

BACKGROUND: Epidemiological evidence suggests that diabetes mellitus (DM) is associated with a decrease in risk for prostate cancer (PCa). The objective of this study was to examine the association between PCa risk and several characteristics of DM (duration, age at diagnosis, treatment) in data from two population-based, case-control studies of PCa.
METHODS: PCa cases (n = 1,752), and controls (n = 1,644) were residents of King County, Washington identified using the Surveillance, Epidemiology, and End Results Seattle-Puget Sound cancer registry and random digit dialing, respectively. The majority of PCa patients had localized stage disease (78%). Using self-reported on DM, logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI) for associations between DM characteristics and PCa risk.
RESULTS: After adjustment for confounding factors, DM status was not significantly associated with PCa risk (OR = 0.98; 95% CI = 0.76-1.27). However, early-onset DM (diagnosed before age 30) showed a significant inverse association with PCa risk (OR = 0.27; 95% CI = 0.07-0.97). Time since DM diagnosis (median = 6 years) and DM treatment types (i.e., diet changes, oral medications, and insulin) did not show significant associations with PCa risk.
CONCLUSIONS: These data suggest that DM is not associated with PCa risk; however, early-onset DM, possibly reflecting insulin dependent DM (type 1), may be an important component of the previously reported inverse association between DM on PCa risk, but these findings are based on a small number of observations and require further investigation. (c) 2008 Wiley-Liss, Inc.