Clinical Use of Prostate Specific Antigen ( PSA )

Like other countries, Japan is recording a rapid increase in the incidence of prostate cancer. The use of serum PSA (prostate specific antigen) measurement as a blood marker for prostate cancer has become widespread. Higher levels of PSA are associated with a higher probability of a diagnosis of prostate cancer. Needle biopsies detect prostate cancer in 20–30% of cases with PSA levels of 4.1–10ng/ml, and 30–50% or more of cases higher than 10ng/ml. All cases showing PSA levels of 4.1ng/ml or more should be referred to specialist urologists, as well as those showing PSA levels of 4.0ng/ml or less and positive findings on digital rectal examination. However, PSA also increases in other conditions such as benign prostatic hyperplasia, prostatitis, and urinary retention, and this fact needs careful attention. In addition, there is a risk that administration of antiandrogen may lower PSA levels and mask the presence of prostate cancer. So-called gray-zone cases with PSA levels of 4–10ng/ml present a problem of differentiation from benign prostatic hyperplasia. Improvement in accuracy has been attempted with various approaches, such as PSA density, PSA free/total ratio, PSA velocity, and age-specific PSA reference ranges. In observation after the treatment of prostate cancer, PSA is useful for the early diagnosis of recurrence