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Overdiagnosis of Invasive Breast Cancer With Mammography Screening FREE

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The full report is titled “Overdiagnosis of Invasive Breast Cancer Due to Mammography Screening: Results From the Norwegian Screening Program.” It is in the 3 April 2012 issue of Annals of Internal Medicine (volume 156, pages 491-499). The authors are M. Kalager, H.O. Adami, M. Bretthauer, and R.M. Tamimi.

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Ann Intern Med. 2012;156(7):I-58. doi:10.7326/0003-4819-156-7-201204030-00001
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What is the problem and what is known about it so far?

Women are advised to get routine mammograms to find breast cancer early, before it would have been noticed on examination. This is called screening mammography. However, some cases of breast cancer found with screening mammography would never have been noticed and therefore would not have led to death.

Why did the researchers do this particular study?

To see how common screening mammography leads to overdiagnosis of breast cancer.

Who was studied?

Women in Norway who had a diagnosis of invasive breast cancer from 1986 to 2005.

How was the study done?

In Norway, screening mammography was introduced or “rolled out” over a decade, county by county. The number of cases of breast cancer found in counties with screening was compared with the number of cases found in counties without screening during the same period.

What did the researchers find?

About 15% to 25% of cases of breast cancer found through routine mammography were overdiagnosed; that is, they would never have been found on examination or led to death.

What were the limitations of the study?

The study included women diagnosed with invasive breast cancer, not those with ductal carcinoma in situ, a different form of breast cancer. The study was not a randomized trial where women were or were not given mammograms depending on chance (like flipping a coin).

What are the implications of the study?

For many women, screening mammography may lead to a diagnosis of breast cancer that would never have been noticed or caused harm during their lifetime. These women would have been unnecessarily treated with therapies, including surgery, radiation, and chemotherapy, that have adverse effects.





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