Purpose: We reviewed the available data on the effect of finasteride o
n serum levels of prostate specific antigen (PSA), PSA velocity and PS
A density in men with benign prostatic hyperplasia (BPH) and prostate
cancer. Materials and Methods: To our knowledge all previously publish
ed analyses of PSA data from clinical trials of finasteride therapy fo
r BPH and prostate cancer are reviewed. Results: The normal reference
range of serum PSA levels in men with BPH and no evidence of prostate
cancer who were treated with finasteride for 6 months or longer is hal
f that in untreated men with BPH. The percent by which serum levels of
PSA are suppressed after 6 months of treatment for prostate cancer do
es not tend to be greater than that for BPH. Conclusions: To interpret
serum PSA levels in men with BPH treated with finasteride for 6 month
s or longer, the serum PSA level should be multiplied by 2 and compare
d to either age-independent or age-specific upper limits of normal for
serum PSA in untreated men with BPH. On the basis of limited data the
sensitivity and specificity of this approach appear to be similar to
those of the corresponding PSA limits in untreated men with BPH.