Prostate-specific antigen and androgen deprivation therapy.

Prostate-specific antigen (PSA) is a kallikrein-like serine protease that, for all practical purposes, is specific for prostatic tissue. PSA is usually detected at low concentrations (0.0-4.0 ng/ml) in the serum and is the most important tumor marker for detecting otherwise unsuspected prostate cancer; it also useful for monitoring the response of prostate cancer to various types of therapy. Androgen deprivation therapy (ADT) includes bilateral orchiectomy, luteinizing hormone-releasing hormone (LHRH) agonists, antiandrogens, and 5-alpha-reductase inhibitors. Treatment of benign prostatic hypertrophy (BPH) or prostate cancer with ADT usually decreases the serum PSA concentration. Recent basic science research has demonstrated that the expression of the PSA gene is controlled by androgens acting via the androgen receptor. Therefore, in some patients a low serum PSA concentration will be the result of hormonal down-regulation of the genetic expression of PSA and not the result of the antitumorigenic activity of the therapy. Nevertheless, in spite of the direct effect of ADT on PSA expression, PSA remains a valuable prostate cancer tumor marker for prognosticating the response to ADT and portending clinical progression after this type of treatment for most patients.