Serum testosterone and the risk of prostate cancer: potential implications for testosterone therapy.

OBJECTIVE A potential risk of testosterone replacement therapy is an increase in the incidence of prostate cancer, but it is unclear whether higher levels of serum testosterone are associated with a higher risk of prostate cancer. We prospectively evaluated serum androgen concentrations and prostate cancer risk. METHOD Included were 794 members of the Baltimore Longitudinal Study of Aging. We estimated the rate ratio (RR) of prostate cancer by entering serial measures of serum total testosterone, dehydroepiandrosterone sulfate, sex hormone binding globulin, calculated free testosterone, and free testosterone index (FTI) into a Cox proportional hazards regression model with simple updating. RESULTS Higher calculated free testosterone was associated with an increased age-adjusted risk of prostate cancer {RRs by quartile: 1.00, 1.52 [95% confidence interval (95% CI), 0.93-2.50], 1.16 (95% CI, 0.61-2.20), 2.59 (95% CI, 1.28-5.25); P(trend) = 0.03}, which persisted after excluding measures in men <45 years of age [RRs by quartile: 1.00, 1.33 (95% CI, 0.78-2.25), 1.26 (95% CI, 0.68-2.33), 1.89 (95% CI, 0.99-3.61); P(trend) = 0.03]. Compared to men with eugonadal FTI (> or = 0.153), men with hypogonadal FTI had a decreased risk of prostate cancer (RR, 0.51; 95% CI, 0.31-0.82). CONCLUSION Higher levels of calculated serum free testosterone are associated with an increased risk of prostate cancer. These findings suggest that men receiving testosterone therapy should be regularly monitored for prostate cancer and underscore the need for prospective trials of testosterone therapy incorporating incidence of prostate cancer as a primary safety end point.