Plasma testosterone and sex hormone-binding globulin concentrations and the risk of prostate cancer among Japanese men: a nested case-control study

Sex hormones, particularly androgens, have been implicated in prostate carcinogenesis. Overall, however, prospective studies have reported no association between circulating levels of sex hormones and the risk of prostate cancer. However, despite the possible difference in the effects of hormones on prostate cancer risk by stage, age, body mass index (BMI) and isoflavones, evidence for these is sparse. Moreover, few studies have been conducted in Asian populations, who are relatively lean and have high isoflavone consumption. We examined the hypothesis that plasma concentrations of circulating testosterone and sex hormone-binding globulin (SHBG) are associated with the risk of prostate cancer in a case-control study nested in the Japan Public Health Center-based Prospective Study. Concentrations of total testosterone and SHBG were measured in plasma samples from 201 patients with prostate cancer and 402 matched control participants, and concentrations of free testosterone were calculated. No overall association between the plasma levels of any hormone and total prostate cancer was observed. Odds ratios (95% confidence interval CI]) in the highest versus lowest group were 0.71 (95% CI = 0.36-1.41, Ptrend = 0.43) for total testosterone, 0.70 (95% CI = 0.39-1.27, Ptrend = 0.08) for free testosterone and 1.38 (95% CI = 0.69-2.77, Ptrend = 0.23) for SHBG. When stratified by cancer stage, age, BMI and plasma isoflavone level, free testosterone was inversely associated with localized cancers and equol producers, while SHBG was associated with an increased risk of prostate cancer in younger men. In conclusion, in this nested case-control study, concentrations of circulating total testosterone, free testosterone or SHBG were not strongly associated with a risk for total prostate cancer.