To screen or not to screen?

31. March 2010

Ever since the implementation of mammography screening on a regular basis, epidemiologists, radiologists and oncologists argue about the effectiveness of such examinations. New results point to the alarm bells ringing much more often than necessary.

October 26, last year, the reputed science department of the New York Times wrote: “Cancers grew and worsened. But data from more than two decades of screening for breast and prostate cancer call that view into question.” Gina Kolata, the editor, referred to an article in the professional magazine JAMA. Laura Esserman director at the breast center of the University of California in San Francisco believes to read out of the figures that screenings for tumors in breast and prostate discovers many small tumors that do not continue growing or even disappear on their own.

More discovered tumors – mortality remains the same

Although the number of positive results has doubled since the mammography screening was implemented, the number of tumors in an advanced stage – just like the share of deaths caused by breast cancer – scarcely decreased. The authors consider the current form of mammography an over-diagnosis, just the PSA-test common in the US supposed to discover prostate tumors. Also in Germany the curve of deaths caused by those two cancers is not taking into consideration bending down but remains level despite a few varying percent. Studies of Peter Gøtzsche in Denmark made for a “Cochrane Review” support this thesis just like a study made in Norway. Women coming three times during six years to get a breast screening showed about 20 percent more tumors than those not able to attend the program and now being checked. From their results, the authors conclude that a significant part of the tumors discovered probably would have disappeared on their own within those six years.

Not only mathematics of the epidemiologists suggests too many unnecessary cancer therapies but also autopsy results of victims of accidents or other diseases. The closer breasts of deceased were examined the more growths were found which obviously did not grow into an aggressive tumor. The former director of the Canadian breast cancer screening initiative Cornelia Baines reports as well about an adenocarcinoma in her breast. It was visible in pictures taken nine years before but back then not recognized as tumor tissue.

Let the small fish swim

Barely growing tumors or even spontaneous remissions also in advanced stages are known in other tumors as well: Gina Kolata reports of several cases of male germ cell tumors which left nothing more behind than a large scar in the testicle tissue after taking a closer look. And the curious journalist will find even more in scientific literature.

Although most experts agreed only several years ago that an intensive screening on a regular basis could decrease the rate of cancer deaths significantly, today this point of view does not apply fully any more. On the contrary they now urge to have some of the money spent more and more for expensive mass screenings in research differentiating aggressive tumors from their peaceful brethren. Martin Gleave, professor for urology at the Canadian University of British Columbia in Vancouver depicts it: “Our net has become that fine that we can catch large but also small fish. Now we should be able to distinguish and decide which small fish we can let go.”

Mammography: Completely overvalued

Elaborate campaigns have attracted many people to visit the physician’s office but also caused many wrong images about the opportunities and possibilities of cancer screening. “I can protect myself against getting breast cancer with mammography.” According to a survey in 2005, about 62 percent of all women going to a breast examination are convinced that this is correct. Gerd Gigerenzer at the Max-Planck Institute for Educational Research in Berlin has made a large European study with about 10,000 participants and the study confirms these statements. About 30 percent of the German women thought that mammography saves more than 100 lives of 1000 breast cancer deaths. Only one percent estimated the actual figures correctly. In one thousand examined women, breast cancer then kills “only” four instead of five victims. Nowhere else in Europe women overvalue the significance of early detection that much. In a similar survey, even the gynecologists were off base: of those 160 physicians interviewed by Gigerenzer regarding the relevance of a positive mammography result, two out of three physicians estimated the probability of a tumor at more than 80 percent. The correct figure: About 10 percent.

Despite all objections against exaggerated expectations, the fewest critics want to scrap the according examinations completely. Instead they plead, just like Gigerenzer, for a “responsible and informed patient” making his or her decision after a careful deliberation of the risks. In addition, epidemiologists like Nikolaus Becker at the Deutsches Krebsforschungszentrum (German cancer research center) believe that an increasing precision of the devices and experience of the physicians will influence and tip the scale at mortality in favor of mammography. After all it is not just about death rates but also getting rid off the tumor with breast preserving methods. And you cannot tar all screening campaigns with the same brush: For other tumors like for example the colon- or the cervix carcinoma, the screenings lead to a “significant decrease of invasive tumors, explain Esserman and Co. in their publication.

Klaus Koch, in previous days a feared sharp analyst at the “Sueddeutsche Zeitung” (German newspaper), and now working at the IQWIG (Institute for Quality and Efficiency in Health Care) writes in an article for the “Onkologen” (oncologists, German publication): “In practice the following rule of thumb can apply: The risk to become a cancer patient unnecessarily is larger than the probability to be saved from dying due to this examination. This statement is proven well mainly for the early detection of breast-, prostate- and cervical cancer.” About four out of ten breast cancer cases are interval carcinomas developing between two examinations and found by the women without mammography – a fact that provides ample food for thought.

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