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Make an Informed Decision about Mammography

Posted by medconsumers on March 1, 2009

A Rare Honest Explanation of the Pros and Cons of Mammography Screening

Printed materials designed to inform women about the need for regular screening mammograms are notorious for not mentioning the harms as well as the benefits of early breast cancer detection. A ground-breaking exception has just been made freely available at the Web site of the Nordic Cochrane Centre of Denmark (click here to view leaflet updated 2012).

The “leaflet” comes from a research team led by Peter C. Gøtzsche, DrMedSci, director of the Nordic Cochrane Centre, Copenhagen, which found that the major risk to screening mammograms is overdiagnosis—that is, unnecessary treatment for a cancer that would never progress. As the new leaflet puts it, “If 2,000 women are screened regularly for 10 years, one will benefit from the screening, as she will avoid dying from breast cancer. At the same time, 10 healthy women will, as a consequence, become cancer patients and will be treated unnecessarily.” No test can accurately distinguish the cancers that will become aggressive from those that will remain dormant or develop very slowly.

This project has a history that dates back to 1999 when Dr. Gøtzsche was asked by a Danish government agency to conduct a systematic review of all mammography screening trials worldwide. The agency wanted to know what the research had actually proven because doubts had been raised about the benefit of screening. This review was eventually published in The Lancet and in the Cochrane Library in 2001, and according to the requirement of the Cochrane Collaboration, it was updated in 2006 and is currently being updated again. The conclusion of the Cochrane review is: “It is not clear whether screening does more good than harm.”

Two of the seven trials in this Cochrane review, one conducted in Sweden and the other in Canada, found no decrease in breast cancer mortality among women given regular mammograms. The other five trials found small reductions in breast cancer mortality among those who had received mammograms. The seven trials had a combined total of about 500,000 women in North America and Europe who had been randomly assigned to receive regular mammograms or not.

The new leaflet’s benefit/harm calculations are based on the combined results of these trials—for every 2,000 women who undergo mammography screening over the course of ten years, one will avoid a breast cancer death and ten more will be treated unnecessarily for a nonprogressive cancer due to overdiagnosis.

The Cochrane review was not well received in this country because it contradicts the prevailing medical wisdom about mammography screening and dared to calculate harms.

In time, Dr. Gøtzsche and colleagues went on to assess the quality of the printed information given to women in six countries with publicly funded screening programs. Such countries inform women of the need for mammograms via “letters of invitations” to be screened. “The major harm of screening, which is overdiagnosis and subsequent overtreatment of healthy women, was not mentioned in any of 31 invitations. Ten invitations argued that screening either leads to less invasive surgery or simpler treatment, although it actually results in 30% more surgery, 20% more mastectomies, and more use of radiotherapy because of overdiagnosis,” wrote Gøtzsche and colleagues in a recent issue of the British Medical Journal.

No such survey of U.S. mammography information sources has been conducted, though a 2000 survey of American women’s attitudes toward this screening test showed 94% doubt the possibility of cancers that do not progress.

To read what is arguably the first honest mammography information for women written by health professionals, go to the Web site of the Nordic Cochrane Centre (, which also provides free access to the Cochrane review. The information is currently being translated into Spanish, Portuguese, Polish, Norwegian, Swedish, Finnish and Icelandic, and there are also plans for German and French translations.

Maryann Napoli, Center for Medical Consumers© March 2009

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