Mammograms tied to overdiagnosis of breast cancer


Widespread breast cancer screening may catch more small, slow-growing tumors that likely to be fatal without curbing the diagnosis of advanced cancer cases, a Danish study suggests.

Diagnosis rates for early-stage tumors and pre-invasive malignancies known as ductal carcinoma in situ (DCIS) have increased in recent years as more women receive screening mammography.

The current study provides fresh evidence that routine screening for the over-diagnosis of non-aggressive tumors because it also compares results for a single period in two regions of Denmark – a, which provided biennial mammography for women aged 50 to 69 and one that is not.

“Overdiagnosis means that healthy women are getting unnecessary breast cancer diagnosis,” said lead study author Dr. Karsten Juhl Jorgensen of the Nordic Cochrane Centre and Rigshospitalet in Copenhagen.

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“A breast cancer diagnosis is a life-changing event for the woman and her family, with significant consequences for their quality of life,” Jorgensen added by e-mail. “It also leads to overtreatment with surgery, radiotherapy and sometimes chemotherapy – we know that this treatments for serious, sometimes deadly consequences.”

The goal of mammography is to tumors to be detected before they can be felt in a physical breast exam, catching cancer earlier when it is easier to treat. Ideally, this should mean that fewer women are diagnosed when tumors are larger, fast growing, and harder to attack.

To see how well mammograms achieve this ideal, researchers examined the data of more than 1.4 million Danish women in the age group of 35 to 84, from 1980 to 2010.

Organized breast cancer screening programs started in Copenhagen in 1991, and Funen in 1993 and Frederiksberg in 1994 – in total covering about 20 percent of the population. Other regions are gradually introduced screening to begin in 2007.

The Screening was not associated with a lower incidence of advanced tumours, researchers report in the Annals of Internal Medicine.

This raises doubts about whether mammography screening reduces breast cancer deaths, the researchers conclude.

In addition, the researchers estimate that as many as one in three breast tumors diagnosed in women who got mammograms would never have led to a noticeable health problem or led to death and are, therefore, examples of overdiagnosis.

A limitation of the study is that because mammography has improved since this study began in 1980, women can get different results today, the authors note.

During the study adds convincing evidence that routine mammograms carry a risk of over-diagnosis, that does not mean that it is time for screening guidelines change, Dr. Otis Brawley, chief medical officer of the American Cancer Society, said in a telephone interview.

Under the current US guidelines, mammograms should be optional for women in the age group of 40 to 44, shall be made annually from 45 to 54. Women of 55 and older should switch to a mammography every two years, as long as they are in good health with a life expectancy of at least ten years.

“This is not about don’t say a mammogram, this is about the use of the most effective to save the most lives,” said Brawley, who wrote an editorial supervision of the study.

Outside the screening, there are other preventive measures that women should not be overlooked, such as good food, enough exercise, and maintaining a healthy weight.

In the future it may be possible to use the screening results to pinpoint women who may be eligible for “watchful waiting” and close follow-up without treatment is common for many people with early stage of prostate cancer, Brawley said.

“We are not yet ready for it, because we do not know what watchful waiting seems to be for breast cancer,” Brawley said.

So for now, that means accepting that overdiagnosis and screening go hand in hand, together with the potential for some women to get unnecessary treatment.

“If it’s small and slow-growing, I think that all breast cancer ought to be treated,” Brawley added.

SOURCE: Annals of Internal Medicine, online January 9, 2017.

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