Norwegian Study Suggests Digital Mammography Reduces False Positives

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For many years, mammograms were done by recording images of the breasts on large sheets of black and white film. As technology advanced, mammograms went digital. In digital mammograms, the images are recorded into a computer. Digital mammograms are thought to offer advantages over film mammograms, including:

  • less radiation exposure per breast image
  • a better breast image, especially in younger women with dense breasts (breasts that have a lower-than-average amount of fat tissue)

Mammograms are the best way for doctors to find cancer early, when it’s most treatable. Still, mammograms aren’t perfect. Normal breast tissue can hide a breast cancer so that it doesn't show up on the mammogram. This is called a false negative. And mammography can identify an abnormality that looks like a cancer, but turns out to be normal. This "false alarm" is called a false positive. Besides worrying about being diagnosed with breast cancer, a false positive means more tests and follow-up visits, which can be stressful.

While digital mammograms are thought to offer advantages over film mammograms, research results have shown that the accuracy of film and digital mammograms is about the same. Experts expected that recall rates -- the rate at which women are called back for more tests because something didn’t look right on a mammogram -- would be lower for digital mammograms than film mammograms. But the rates have varied widely among studies.

To help figure out if digital mammograms have a lower recall rate than film mammograms, Norwegian researchers looked at information from a national breast cancer screening program in that country. The Norwegian Breast Cancer Screening Program invites women ages 50 to 69 to have a mammogram every 2 years.

The research was published online on April 1, 2014 by Radiology. Read the abstract of “Mammographic Performance in a Population-based Screening Program: Before, during, and after the Transition from Screen-Film to Full-Field Digital Mammography.”

When new technology such as digital mammography is introduced, it usually takes some time for all doctors to learn how to use the technology and be confident in its results. The Norwegian researchers suspected that during the transition period from film to digital mammograms, some doctors ordered more tests just to make sure the digital mammograms were producing accurate results. They thought this transition period might have been affecting the results of earlier studies comparing the recall rates of digital and film mammograms. So they decided to review screening results from before, during, and after the switch to digital mammograms.

The researchers looked at results from more than 1.8 million mammograms done from 1996 to 2010. The results include women screened:

  • only with film mammograms
  • only with digital mammograms
  • with both film and digital mammograms

They then compared:

  • the rate of breast cancer cases
  • recall rates
  • the rate of mammogram-detected breast cancer
  • the rate of breast cancers found within 12 months after a normal mammogram (doctors call these “interval breast cancers”)

Overall, the recall rates were:

  • 3.4% for film mammograms
  • 2.9% for digital mammograms

About 1.4% of the women who had a film mammogram had a biopsy and about 1.1% of the women who had a digital mammogram had a biopsy.

To judge the accuracy of a test, doctors sometimes use a measure called “the positive predictive value.” This is the likelihood that patients with a positive test actually have the disease. In this study, the positive predictive value of additional tests and biopsies went up after the switch to digital mammograms:

  • the positive predictive value of additional tests went from 19.3% to 22.7%
  • the positive predictive value of biopsies went from 48.3% to 57.5%

This means that digital mammograms had fewer false positive results than film mammograms.

Other research has shown that digital mammograms are more accurate than film mammograms in finding breast cancer in women who:

  • are younger than 50
  • have dense breasts
  • haven’t gone through menopause

The risk of a false positive isn’t a good reason to skip getting an annual mammogram. If you're 40 or older and have an average risk of breast cancer, yearly screening mammograms -- either digital or film -- 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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