Improving PSA for Diagnosis
PSA (Protate Specific Antigen) is extremely valuable in detecting prostate cancer at earlier more curable stages. However, PSA is only prostate specific, not cancer specific. That means that there are other prostate problems that can cause your PSA to increase, e.g. infections, benign prostatic hyperplasia (BPH), and instrumentation. To solve this problem we recently demonstrated a simple means to improve the specificity of PSA in distinguishing cancer from these other causes by measuring the rate of change in serum PSA levels from one year to the next.
This discovery was based upon some very simple principles. First, the amount of PSA in the serum produced by 1 gram of cancer is 10 times higher than the amount of serum PSA produced by a similar amount of benign disease. Second, the growth rate of prostate cancer is much more rapid than the growth rate of BPH. We therefore reasoned that yearly changes in serum PSA should be much greater in men with cancer than in men with BPH. This theory was tested using the large group of men who are enrolled in the Baltimore Longitudinal Study of Aging. Since 1958, 1500 men have returned every other year to undergo an extensive examination and storage of blood samples. We were able to obtain blood samples from age matched men with prostate cancer, BPH, and no prostate disease, who had blood samples stored for almost 20 years prior to diagnosis. We were able to demonstrate that 5 years prior to standard diagnosis, the yearly increases in serum PSA in men with prostate cancer were greater than in men with BPH or no prostate disease. Based upon these findings, we feel that any man who has a consistent increase (over 3 determinations) in his serum PSA of greater than 0.75 ng/ml per year runs a strong likelihood of having prostate cancer. Using this formula we were able to identify 75% of the men with cancer and only falsely classified 10% of the men with BPH and none of the men with no prostate disease. We feel that this concept will make it possible to identify prostate cancer with greater specificity and at lower levels of serum PSA than using the current established upper limit of normal of 4.0 ng/ml. It is possible that this technique may also make it possible to identify those cancers that are growing and require treatment.
- Carter, H.B., Pearson, J.D., Metter, J., Brant, L.J., Chan, D.W., Andres, R., Fozard, J.L., and Walsh, P.C.: Longitudinal evaluation of prostate-specific antigen levels in men with and without prostate disease. JAMA 267:2215-2220, 1992.