Measuring Free PSA Can Help Stage and Classify Prostate Cancer

Testing further for a form of prostate-specific antigen (PSA) can help urologists find, stage, and classify prostate cancer in men whose PSA tests are ambiguous, according to a multicenter study that included The Johns Hopkins Hospital. The additional test, which is routinely available for all men taking the PSA test, can also help patients and their doctors determine the best course of treatment. The test measures free PSA, the form of PSA not bound to proteins in the blood. According to the study, the higher the percentage of free PSA compared to the bound form, the smaller the tumor is likely to be, the less chance there is that it has spread from the prostate, and the less likely it is that the disease is the most aggressive form.

The study was reported in the October 1999 issue of The Journal of Urology.

Staging Dilemmas

At least one-third of localized cancers are understaged. The current staging technique combines PSA tests with digital rectal examinations, transrectal ultrasound, and biopsy Gleason grades. The most popular assessment of whether the tumor has spread beyond the prostate involves a nomogram that measures PSA, clinical staging, and Gleason score. Earlier studies showed that a small percentage of free PSA in the blood is associated with the more aggressive forms of prostate cancer.

Study Data

The study, involving seven medical centers, looked at 379 men with prostate cancer and 394 with benign prostatic disease. The men all fit into a gray diagnostic area: they had negative digital rectal examinations but their PSA level was between 4.0 and 10.0 ng/mL and 75% had negative biopsies.

The men in the study ranged from 50 to 75 years of age (median age was 62 years). The study found that a higher percentage of free PSA was associated with more favorable histopathologic findings. The lower the percentage of free PSA, the larger and more advanced the tumor was likely to be, with a milestone set at 15%.

The researchers concluded that the percentage of free PSA could be used for diagnosis and staging. Patients with more than 25% free PSA probably did not need a biopsy unless they had a family history of prostate cancer. Also, patients with more than 15% free PSA had the most favorable outcomes. Using free PSA would detect 95% of cancers and spare 20% of men with benign disease from having to undergo biopsies.

Beckman Coulter provided financial aid for the study.