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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.
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