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Risks and Benefits of Mammography Screening


Screening for breast cancer with mammography is offered to older women at no cost by health insurance in many countries. Mammography is an x-ray examination of the human breast and aims to increase the chance of recovery by detecting existing tumors as early as possible. But what is the actual benefit of mammography screening and how frequent are potential harms? And would participating in the screening be advisable for you?
 

Medical questions often have no clear-cut answers. For this reason, transparent information is crucial - as is the courage to make informed decisions oneself. To help you weigh the pros and cons of mammography screening, we have prepared a fact box with neutral and easy-to-understand information about its harms and benefits.

The numbers refer to 1,000 women over 50 years of age* who participated in the screening for 10 years (screening group), compared to 1,000 women of the same age who did not participate in the screening during the same time period (control group).

 

faktenbox_mammographie

 

The fact box shows that mammography screening reduced the number of deaths through breast cancer from 5 to 4 in 1,000 women. This effect had no influence on all-cancer mortality: The number of women who died of any cancer was the same in both groups.

100 of 1,000 women in the screening group had at least one suspicious screening result within the 10 years, though it later proved to be a false alarm. Some of these women had to live with this uncertainty for months and had to go through further diagnostic testing until the all-clear could be given.

Mammography screening also detects so-called "indolent" (slowly growing or less aggressive) tumors, which would never develop into a life-threatening disease. But because their development cannot be predicted, about 5 of 1,000 women in the screening group unnecessarily had their breast completely or partially removed.

Unfortunately, few reliable studies to date have investigated mammography screening. The numbers in our fact box are taken from a systematic review of these studies and hence offer the best evidence available. Nevertheless, the numbers should not be seen as definitive but instead as roughly conveying the extent of possible benefits and harms.

* The numbers for breast cancer mortality refer to women above 50 years of age. Because no other data are available, all further data in the fact box are based on studies that also included women above 40 years of age.

 

Source:
Gøtzsche PC, Nielsen M. Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2011, Issue 1. Art. No.: CD001877. DOI: 10.1002/14651858.CD001877.pub4

The authors distinguish between better and suboptimal studies. In the better studies it was found that only a non-significant absolute reduction of 0.3 deaths per 1000 women from breast cancer occurred, whereas the suboptimal studies found a reduction of 2.1 deaths per 1000 women. Favoring the better studies, the authors estimated the total reduction to be 0.5 out of 1000 women. The more generous estimate in the fact box is 1 out of 1000, which is the (rounded) average of the reductions in the better and the suboptimal studies.

 >> plain languange summary of the study on Cochrane.org

The idea of fact boxes was developed by Lisa Schwartz and Steven Woloshin. In several studies they demonstrated that fact boxes are effective tools for informing the general public about harms and benefits of medical treatments. Read more in the overview.