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| Is it Really Possible to Test Too Much for Cancer?
"Cartoons and Poems following each article are created and copyrighted by Dr. Ackerman and cannot be copied or reproduced without his permission."
How would you accept a statement from your doctor that you're better off testing for cancer less frequently? If we are to believe a study called "Overdiagnosis due to prostate-specific antigen screening: Lessons from U.S. prostate cancer incidence trends" reported in the Journal of the National Cancer Institute in its July 3, 2002 issue by Etzioni and her colleagues, some physicians may well arrive at that conclusion. After going over the rather fuzzy concepts and conclusions inherent in this article I am still at a loss as to the exact significance of it all. It appears that the study was instituted because; during the decade from 1988 to 1998 epidemiologists had noticed an increased incidence of prostate cancer. Usually, whenever such a dramatic increase occurs, attempts are made to explain why. One commonly proposed possibility is that there was really no true increase; just better diagnostic capabilities available thereby enabling investigators to increase the number of cases detected. Obviously, this seems to be a good thing. Why object to finding more cases, earlier?
According to Etzioni's group, use of the prostate specific antigen (PSA) test actually leads to over diagnosis. Now why would anyone object to over diagnosis as long as cancer was actually detected? Well, the reasoning goes like this: Prostate cancer very often fails to do anything more than just sit there, cause no symptoms, and show up only if an autopsy is done. If the patient will, more than likely, die from something else before the prostate cancer can do him in, why look for trouble in an attempt to find a small tumor unlikely to threaten life and then proceed with unnecessary, risky surgery for an old man?
Over diagnosis was defined as finding cancers that would only have been detected if an autopsy were done. In order to verify that there really was over diagnosis, the investigators developed a computer simulation model of PSA testing along with subsequent cancer diagnosis, and eventual death from the prostate cancer. They then went back to records of two million men who were 60-84 years of age in 1988. Using their findings to develop a projection of the increase in population incidence associated with PSA testing they compared these results with the actual incidence as derived from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) registry data.
According to their results, when prostate cancer is diagnosed only at autopsy, at most 15% of whites and 37% of blacks are over diagnosed. In other words, the PSA screen is detecting these tumors alright, but they would not have harmed the patient for the rest of his life. Reversing this, they ended up by concluding that most cases, the remaining 85% and 63%, detected by screening with PSA would have eventually shown up as cancer before the patient died.
Furthermore, only a minority of cases found at autopsy would have been detected by PSA testing. On the other hand, according to the original SEER data, using PSA for screening results in over diagnosis in about 29% of whites and 44% of blacks. This means that a great number of individuals who have been diagnosed with cancer by means of the PSA will end up dying from some other condition.
So what should you, the patient, get out of all this? Okay, it's true that a lot of people who routinely go for PSA screening and eventually find out that they have cancer won't actually die from that cancer but from something else. I don't know about you, but personally, I prefer not to take my chances that I could be fortunate enough to be one of the few to get away with it. One question that apparently wasn't addressed concerned what was done when these cancers were detected? If PSA saved time so that the cancers were less advanced, then that could explain why many cases didn't die from prostate cancer. Since most cases detected by PSA do end up as cancer, it seems evident that routine PSA screening is the right thing to do, even if a certain amount of over diagnosing occurs. What was so weird about the presentation of this article was that the initial impression is that PSA testing may be overdone. However, careful analysis of what's being said indicates that routine testing is probably the right approach, even if there is a fair amount of surgical risk from removing a tumor detected by the PSA, test, which could last a lifetime without causing any trouble, and even if it results in a certain amount of over diagnosing.
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PSA, DNA, ASA, and AAA,
Whatever they mean, whose to say,
Better look 'em up real quick, okay,
Or I'll never be a member of the AMA.
ACE, APE, BSE, and DOE,
None of 'em mean a thing to me,
Goodness knows I'm up a tree,
I'll never get credit for my CME.
DTR, FHR, GFR, and IVR,
Seems to me they've gone too FAR,
Just hand me the KEYs to my BMW CAR,
Think I'll have a few SIPs at the BAR.
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Cartoons and Poems following each article are created and copyrighted by Dr. Ackerman and cannot be copied or reproduced without his permission.
Copyright © 2007 by Marvin Ackerman, M.D.
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