HealthDay News — According to a new study published in the Annals of Internal Medicine, mammograms frequently detect small breast tumors that might never become life-threatening — causing women to receive treatment they likely don’t need.

Karsten Juhl Jorgensen, MD, deputy director of research for the Nordic Cochrane Center at the Rigshospitalet in Copenhagen, Denmark, and colleagues used data from two comprehensive Danish cancer registries to check the effectiveness of breast cancer screening. 

They reviewed the medical records of all Danish women diagnosed with invasive breast cancer between 1980 and 2010. 

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The researchers compared the incidence of advanced tumors in women aged 50 to 84 in areas that had adopted regular breast cancer screening against areas that did not regularly screen. They also compared the detection of small, non-advanced tumors among women in several age categories: 35 to 49, 50 to 69, and 70 to 84.

The researchers found that about 1 in every 3 women between the ages of 50 and 69 who were diagnosed with breast cancer had a tumor that posed no immediate threat to her health.

At the same time, mammography did not reduce the number of advanced breast cancers found in women in the study. The team estimated that between 14.7 to 38.6% of breast cancers were overdiagnosed.

“This means that breast screening is unlikely to improve breast cancer survival or reduce the use of invasive surgery,” Jorgensen told HealthDay. “It also means that breast screening leads to unnecessary detection and treatment of many breast cancers.”


Jørgensen KJ, Gøtzsche PC, Kalager M, Zahl P. “Breast Cancer Screening in Denmark: A Cohort Study of Tumor Size and Overdiagnosis.” Ann Intern Med. doi: 10.7326/M16-0270. [Epub ahead of print] 

Brawley OW. “Accepting the Existence of Breast Cancer Overdiagnosis.” Ann Intern Med. doi: 10.7326/M16-2850. [Epub ahead of print] 

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