Prostate-specific antigen and prostate cancer.

Serum prostate-specific antigen (PSA) measurement is used to investigate patients with lower urinary tract symptoms and to screen for prostatic malignancy in symptom-free males over 50 years of age. Approximately 60% of patients with early (prostate-confined) occult malignancy show increased serum PSA levels, as do some 20% of patients with prostatic symptoms from benign prostatic disease. When PSA is only slightly raised, serial PSA measurements, correction for prostatic volume and especially measurement of free (unbound) PSA (which is reduced in prostatic malignancy) may assist the differentiation of prostatic cancer from benign hypertrophy. Serial measurements are also of value for monitoring treatment of prostate cancer and for post-treatment surveillance.