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Another Look at Data Finds Mammography Benefits More Consistent Than Reported

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Several large studies, including a review by the U.S. Preventive Services Task Force in 2009 and a study on the causes of death in the United Kingdom in 2013, have questioned the value of screening mammograms.

Doctors who question the value of mammograms say that while mammograms do save lives, for each breast cancer death prevented, three to four women are overdiagnosed. Overdiagnosis means either:

  • a screening mammogram finds a suspicious area that would have been eventually diagnosed as cancer by other means, without any effect on prognosis
  • a screening mammogram finds a suspicious area that never would have affected a woman’s health if it hadn’t been found or treated

False positive results from screening mammograms also have helped fuel the debate about the value of breast cancer screening. When a mammogram shows an abnormal area that looks like a cancer but turns out to be normal, it’s called a false positive. Ultimately the news is good: no breast cancer. But the suspicious area usually requires follow-up with more than one doctor, extra tests, and extra procedures, including a possible biopsy. There are psychological, physical, and economic costs that come with a false positive.

These studies and the resulting stories in the media have fueled an ongoing debate about the value of screening mammograms. To help settle the discussion, a group of researchers from around the world reexamined the data from four large studies on the risks and benefits of breast cancer screening. They found that the benefits of screening mammograms are more consistent across the four studies than has been previously reported. They also found that all the studies showed a sizable reduction in deaths from breast cancer because of screening mammograms.

The study, “Disparities in the estimates of benefits and harms from mammography: Are the numbers really different?,” was presented on Dec. 11, 2013 at the 2013 San Antonio Breast Cancer Symposium. Study results also were published in the November 2013 issue of Breast Cancer Management. The article was titled “Real and artificial controversies in breast cancer screening.”

The four studies the researchers reviewed were:

  • the Nordic Cochrane review
  • the U.K. Independent Breast Screening review
  • the U.S. Preventive Services Task Force review
  • the European Screening Network review

Each one figured out how many women would need to be screened to prevent one breast cancer death. The results ranged from 111 to 2,000, a difference of almost twentyfold. This is important because the more women that need to be screened, the more overdiagnoses and false positives there will be.

The researchers wanted to know if these differences were real or if they were due to differences in the way each study was done. So the researchers looked at the particulars of each study. They found that the studies differed dramatically in terms of:

  • age of the women being screened
  • screening periods
  • follow-up periods
  • number of women invited to be screened versus number of women actually screened

Because of these differences, the studies weren’t comparing the same things. Instead of comparing apples to apples, they were comparing apples to oranges to bananas to grapefruit.

So the researchers standardized all the studies. This means they converted each study so it looked at the effect of screening mammograms on breast cancer deaths for 20 years in women ages 50 to 69.

When they did this, the difference in the number of women needed to be screened to prevent one breast cancer death dropped dramatically. The number ranged from 64 to 257 instead of the original 111 to 2,000. This underscores other results showing that screening mammograms are a valuable tool to save lives.

“The debate about the value of mammography screening is not likely to fade away, and there are real, reasonable differences of opinion about various aspects of screening,” said Robert Smith, Ph.D., senior director of cancer screening at the American Cancer Society, who presented the study in San Antonio. “However, we hope these findings reassure clinicians and the public that there is little question about the effectiveness of mammography screening, which should continue to play a very important role in our efforts to prevent deaths from breast cancer.”

If you're 40 or older and have an average risk of breast cancer, yearly screening mammograms should be part of your healthcare. If your breast cancer risk is higher than average, you should talk to your doctor about a more aggressive breast cancer screening plan that makes the most sense for your particular situation.

There's only one of you and you deserve the best care possible. Don't let any obstacles get in the way of your regular screening mammograms:

  • If you're worried about cost, talk to your doctor, a local hospital social worker, or staff members at a mammogram center. Ask about free programs in your area.
  • If you're having problems scheduling a mammogram, call the National Cancer Institute (800-4-CANCER) or the American College of Radiology (800-227-5463) to find certified mammogram providers near you.
  • If you find mammograms painful, ask the mammography center staff members how the experience can be as easy and as comfortable as possible for you.

For more information, visit the Mammograms pages.

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