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Screening Tests for Prostate Cancer – What's the Best Tool?
Prostate cancer is the most common cancer in adult men and early detection is our best weapon against it.
Much has been written in the press over the past 10 years about prostate specific antigen (PSA) and its effectiveness in detecting prostate cancer. But some recent articles are critical of PSA and suggest that it may be inaccurate. Perhaps the testing has become a victim of its own success and is expected to be more than it is capable of being. Despite the questions, at the present time PSA is still the best single test for prostate cancer screening.
PSA is a protein made by cells in the prostate. As its name implies it is specific only for prostate cells. Therefore, women do not have PSA. It is not made in liver, colon, lung or any other cells in the body. In fact, it is the only blood-born marker that is specific for a particular organ. It is not, however, specific for prostate cancer.
Normal and cancerous prostate cells make PSA. Yet we are able to utilize PSA levels in the blood to detect prostate cancer because men with prostate cancer tend to have higher levels of PSA than men without it. Also, the amount of PSA in the blood rises more rapidly per year among men with prostate cancer, even when the total amount of PSA measured is within the normal range for a particular age group. The argument against PSA is that not everyone with an elevated PSA will be found to have prostate cancer and some prostate cancers found may not be the dangerous variety.
Screening for cancer implies measuring something in a large number of people, looking for a variation that indicates the cancer is present. A test used for screening must be simple, easy to use and cost effective. The ultimate test to determine cancer is a biopsy. The closer a screening test comes to the biopsy results, the better.
In an effort to refine the accuracy of PSA tests, we have found over the years that nuances of PSA expression can be helpful. Your physician will follow the rate of change of PSA over time (aka PSA velocity and PSA doubling time) when checking your yearly PSA results. The amount of PSA bound to other proteins in the blood (aka percent free PSA and complex PSA) and the level of PSA in relation to the size of your prostate (aka PSA density) can help in certain circumstances to select those PSA elevations caused by cancer. A new derivative of free PSA called pro-PSA appears to be more specific for prostate cancer, but the test needs further research to confirm these results.
Because 20 percent of men with prostate cancer have a normal PSA value, the digital rectal examination is also an important tool in detecting prostate caner. A family history of prostate cancer (especially in a first-degree relative) is a significant warning sign to be on the lookout and to begin screening at an earlier age.
The ideal method for detecting prostate cancer would be a simple blood test that was highly specific for prostate cancer only. Just such a test may soon be available. A new protein found only in prostate cancer cells, called early prostate cancer antigen–2 (EPCA–2) has recently been discovered. This substance can be measured in blood. If further studies confirm the early findings it may become the most important tool for detecting prostate cancer.
In the meantime, an annual PSA blood test and digital rectal exam remain the best tools for prostate cancer detection. Start screening by age 50 and certainly earlier if you have a family history of prostate cancer. Normal values for PSA differ by age, and an increase of greater than 0.7 in one year may be significant. If this occurs, consult a urologist for a full evaluation.
PSA Normal Values by Age
|Up to 50 years of age||Not above 2.5|
|50-60 years of age||Not above 3.5|
|60 years of age or older||Not above 4.0|
Michael T. Macfarlane, M.D., is a clinical associate professor of urology at the University of Louisville, School of Medicine . He graduated from the College of Physicians & Surgeons, Columbia University ; trained in general surgery at Harvard Medical School , Brigham & Women''s Hospital in Boston and in urologic surgery at UCLA. He is the author of one of the most popular handbooks of urology for medical students and residents around the world. He practices with Urology Care, LLC and specializes in the diagnosis and treatment of prostate cancer.