Purpose: Diabetes is associated with lower risk of prostate cancer. Most men with diabetes are obese, and obesity is associated with greater prostate cancer mortality. Whether diabetes influences outcomes after prostate cancer diagnosis is unknown.
Patients and methods: We assessed the relationship between prevalent diabetes and mortality using data from Radiation Therapy Oncology Group Protocol 92-02, a large randomized trial of men (N = 1,554) treated with radiation therapy and short-term versus long-term adjuvant goserelin for locally advanced prostate cancer. Regression and proportional hazard models were performed to evaluate relationships between prevalent diabetes and all-cause mortality, prostate cancer mortality, and non-prostate cancer mortality. Covariates included age, race, tumor stage, Gleason score, prostate-specific antigen, weight, and treatment arm.
Results: There were a total of 765 deaths; 210 (27%) were attributed to prostate cancer. In univariate analyses, prevalent diabetes was associated with greater all-cause mortality and non-prostate cancer mortality but not prostate cancer mortality. After controlling for other covariates, prevalent diabetes remained significantly associated with greater all-cause mortality and non-prostate cancer mortality (hazard ratio [HR] = 2.12; 95% CI, 1.69 to 2.66; P < .0001) but not prostate cancer mortality (HR = 0.80; 95% CI, 0.51 to 1.25; P = .34). In contrast, weight was associated with greater prostate cancer mortality (HR = 1.77; 95% CI, 1.22 to 2.55; P = .002) but not all-cause or non-prostate cancer mortality.
Conclusion: Weight but not prevalent diabetes is associated with greater prostate cancer mortality in men receiving combined modality treatment for locally advanced disease. These observations suggest that the association between obesity and greater prostate cancer mortality is mediated by mechanism(s) other than the characteristic metabolic alterations of diabetes.