In 1986, the U.S. Food and Drug Administration approved the prostate specific-antigen (PSA) test as a way to monitor prostate cancer progression. The test measures the amount of PSA in a man’s blood; higher levels of PSA may indicate the presence of prostate cancer. By testing PSA levels, doctors hope to catch prostate cancer in its early stages and treat it. But there are several problems with this plan: (1) PSA levels can be elevated for reasons other than prostate cancer, (2) some prostate cancers will never grow enough to cause problems before a man dies of another cause, and (3) treatments for prostate cancer can lead to other problems, such as impotence and urinary incontinence.
Because rates of prostate cancer diagnosis have risen since the advent of the PSA test, some researchers wonder whether the PSA test is identifying cancers that would not normally have been diagnosed or caused symptoms. Research published in the July 3, 2002 issue of the
Journal of the National Cancer Institute
suggests that PSA testing has led to overdiagnosis of prostate cancer. This means that the PSA test may be diagnosing a significant number of prostate cancers that would not have been diagnosed within a man’s lifetime without the PSA test.
Researchers from several U.S. institutions developed a computer model of PSA testing, prostate cancer diagnosis, and death rates between 1988 and 1998. The model was based on data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results registry and annual PSA testing rates from Medicare claims files. Using this data, a study population was created consisting of 2 million men who were between the ages of 60 and 84 in 1988.
First, researchers identified men who were diagnosed with prostate cancer within three months after having a PSA test. Using sophisticated statistical methods, they estimated the number of these men who were given a PSA test to confirm a prostate cancer diagnosis rather than to screen for prostate cancer. They then used other statistical methods to estimate lead time—the length of time elapsed between PSA detection of prostate cancer and the actual time the prostate cancer would have been diagnosed had the men not had PSA tests.
Using these calculations, researchers estimated the percentage of men diagnosed by the PSA test who would never have been diagnosed with prostate cancer in their lifetimes.
According to this computer model, 29% of white men and 44% of black men were overdiagnosed with prostate cancer, meaning that the PSA test detected a prostate cancer that would not have been detected by other means before the men died of some other cause.
Although these results are interesting, this study has its limitations. Since estimating values such as lead time and the reason for PSA test (screening vs. confirmation of diagnosis) using statistical methods requires a number of assumptions, it is always imprecise. While computer modeling of this kind is helpful for identifying potential trends that warrant further investigation in controlled studies, it cannot be used to form firm conclusions about the proper role of screening.
Is the PSA test a useful tool for prostate cancer detection? This study suggests that the PSA test does, in fact, identify early prostate cancers. However, these findings also add to growing evidence that some prostate cancers, if left untreated, may not progress to a point where they cause symptoms or ill health within the man’s lifetime. Because treatments for prostate cancer can lead to impotence and urinary incontinence, it’s not necessarily in a man’s best interest to treat early stage prostate cancer. Unfortunately, at this point, there is no reliable way to tell which prostate cancers will go on to cause harm and which will not.
An important message from this study is that a PSA test result that is suggestive of prostate cancer does not necessarily mean you need to begin treatment. If your PSA results indicate prostate cancer, talk with your doctor about your options. And feel free to get a second opinion about what your best course of action is. The jury is still out on how to deal with very early stage prostate cancers detected by the PSA test.
Etzioni R, et al. Overdiagnosis due to prostate specific-antigen screening: lessons from U.S. prostate cancer incidence trends.
Journal of the National Cancer Institute.
July 3, 2002;94(13):981-990.
Yao S and Yao G. Understanding and appreciating overdiagnosis in the PSA era.
Journal of the National Cancer Institute.
July 3, 2002;94(13):958-960.
Last reviewed Jul 18, 2002
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