Cook MB, Beachler DC, Parlett LE, et al. - Using a large US commercial insurance research database, experts ascertained if testosterone therapy (TT) alters prostate cancer risk. During 2007 to 2015, men ages 30 years or greater who were new users of TT from the HealthCore Integrated Research Database were selected. Findings revealed that the adjusted prostate cancer IRR was 0.77 when comparing TT with the unexposed group and 0.85 in comparison with the phosphodiesterase type 5 inhibitor (PDE5i) group. Compared with the unexposed or PDE5i comparison groups, men who received TT did not have a higher rate of prostate cancer. The inverse association of TT with prostate cancer can result from residual confounding, contraindication bias, or undefined biological effect.