Association of diabetes mellitus with prostate cancer: nested case-control study (Prostate testing for cancer and treatment study).
Turner EL., Lane JA., Donovan JL., Davis MJ., Metcalfe C., Neal DE., Hamdy FC., Martin RM.
Observational studies suggest that diabetes is associated with a decreased risk of prostate cancer, but few are population based or have investigated associations with cancer stage or duration of diabetes. We report a case-control study nested within the population-based Prostate testing for cancer and Treatment (ProtecT) study ISRCTN20141297. Men aged 50-69 years based around 9 UK cities were invited for a prostate-specific antigen (PSA) test between June 2002 and November 2006. Amongst 55,215 PSA-tested men, 1,966 had histologically confirmed prostate cancer; of these, 1,422 (72.3%) completed the questionnaire and 1,291 (65.7%) had complete data for analysis. We randomly selected 6,479 age- (within 5 years) and general practice-matched controls. The prevalence of diabetes was 89/1,291 (6.9%) in cases and 555/6,479 (8.6%) in controls. Diabetes was associated with a reduced risk of prostate cancer (odds ratio = 0.78; 95% confidence interval: 0.61-0.99). There was weak evidence that the inverse association was greater for well- versus poorly differentiated cancers (p = 0.07). The magnitude of the inverse association did not change with increasing duration of diabetes (p for trend = 0.95). Diabetes is associated with a decreased risk of PSA-detected prostate cancer. These data add to the evidence of the association of diabetes with prostate cancer in the PSA era.