High levels of endogenous gonadal steroids are considered to be risk factors for prostate cancer. However, while the association of sex steroids with prostate cancer is supported by biological evidence, epidemiological studies have reported inconclusive data. Analytical studies using direct measurement of serum steroid levels in relation to prostate cancer risk have shown inconsistent results. Measurement of endogenous hormones in blood or urine poses many methodological and logistic problems, including variations in biological specimen collection and assay methods. These problems may explain, at least in part, the inconsistency of previous study results.
In specific tissues of the body, including prostate, the balance between androgens and estrogens may differ significantly from that in the plasma, being dependent upon the presence and activity of steroid-metabolizing enzymes, such as 5a-reductase and aromatase.