Diabetes Mellitus and the risk of prostate cancer

Background: Little is known about etiologic factors for prostate cancer. Several studies have suggested a protective effect of diabetes mellitus oil the risk of prostate cancer, though a study by our group has found all elevated risk of prostate cancer following ischemic heart disease. Purpose: The purpose of this study was to investigate the association of diabetes mellitus with prostate cancer in the same setting in which we had found all elevated risk following ischemic heart disease. Our study differed from prior studies in utilizing a multi-racial population. Another purpose was to investigate stage-specific effects. Methods: We conducted a hospital-based case-control study in our University Medical Center in New York City. Cases were patients with prostate cancer seen at our Medical Center between January 1, 1984 and December 31, 1986. All cases were histologically diagnosed and had undergone a biopsy or surgical procedure at Columbia-Presbyterian Medical Center (CPMC). The controls were patients who underwent a surgical procedure for benign prostatic hypertrophy (BPH) during the same time frame and were not found to have prostate cancer. Prior history of diabetes was determined by review of the medical records. Logistic regression was used to assess the association between prior history of diabetes mellitus and prior history of prostate cancer. Results: We compared 320 cases to 189 controls, and found a lower risk for prostate cancer in diabetics overall (adjusted Odds Ratios (OR) 0.6, 95% Confidence Interval (CI) 0.3-1.1), though it was not statistically significant. No association was seen with Stage A prostate cancer, but there was a significant reduction in risk for stages B, C, and D combined (adjusted OR 0.47, 0.2-0.9). This effect appeared to be mainly concentrated among whites and Hispanics. Conclusions: Diabetics appear to have a lower risk of prostate cancer, though this effect may be limited to whites. An understanding of this association and its race specificity way help to explain the major difference in incidence rates for prostate cancer between blacks and whites.