[Prostate-specific Antigen or PSA. Facts and Probabilities]

The introduction of prostatic specific antigen (PSA) assay as an organ-specific marker has totally modified our approach to diseases of the prostate gland. PSA is an exocrine secretion of the normal epithelium of the prostate and any infectious, dystrophic or tumoural processes involving the gland can lead to an increased level in the blood stream. PSA is the most effective means of following the curative effect of treatment for prostate cancer. After radical prostatectomy, PSA should be undetectable with hypersensitive tests (detection threshold < 0.1 ng/ml) 6 weeks after the operation. The persistence or reappearance of the marker in the blood stream is a clear indication of recurrence. A drop off in PSA under laboratory normal levels is an effective marker of the efficacy of hormone treatment for metastatic cancer but does not signify cure. There are still several points of debate. Serum PSA does increase with prostate volume but there is no apparent linear relationship. PSA is an important factor in early diagnosis of prostate cancer but must always be interpreted in light of the patient's age. In patients treated for cancer of the prostate, PSA is insufficient to determine tumour extension. The relationship between the PSA level and prostate volume could be a way of suspecting cancer, but the operator-dependent results of echography hinder application. Finally, search for circulating secretory cells with reverse transcriptase polymerase chain reactions still requires validation, but could be used for assessing cancer extension.