Annual Mammograms Find Cancer Earlier, but Cause More False Positives

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In November 2009, the U.S. Preventive Services Task Force (USPSTF) recommended that routine screening mammograms for women with an average risk of breast cancer should start at age 50, instead of age 40. These recommended changes were very controversial and were not adopted. U.S. guidelines call for all women age 40 and older to have screening mammograms every year. While not ideal, some women may choose to have a screening mammogram every other year.

A study in the Oct. 18 issue of the Annals of Internal Medicine found that when women start getting yearly mammograms at age 40 about 61% of them will be called back for more imaging tests because the mammogram showed an abnormality that looked like cancer but turned out to be normal. This 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.

About 7% of women will have a biopsy because of a false positive.

When women were screened every other year, as the USPSTF recommended, though starting at age 40, about 42% of women needed more tests because of a false positive and about 5% had a biopsy because of a false-positive. But screening every other year also meant that more breast cancers were diagnosed at an advanced stage: 3.3% more in women in their 40s and 2.3% more in women in their 50s.

Some experts feel that the USPSTF had good intentions, but could have written the recommendations more clearly. Some experts believe that most women between age 40 and 50 who have all the information about screening mammograms' benefits and risks will choose to be screened; so routine screening makes sense. Other experts believe that the biggest risk of screening between age 40 and 50 is over-diagnosing and unnecessarily treating abnormal areas that wouldn't have become a health threat. This study supports those experts' beliefs. believes that all medical decisions, including if and when to screen for breast cancer, are decisions to be made by each woman and her doctor. is still concerned about the USPSTF recommendations, since saying that women age 40 to 50 don't need routine screening mammograms could discourage women in that age group from getting mammograms. The recommendation also could have meant that insurance companies might not cover mammograms done before age 50. Fortunately, the U.S. Congress passed legislation so that will not happen.

Another study by the same researchers found that overall, digital mammograms and film-screen mammograms both detected about the same number and types of cancers. This study also was published in the Oct. 18 issue of the Annals of Internal Medicine.

Film-screen mammograms record black-and-white images on large sheets of film. Digital mammography records images directly into a computer. The image can then be viewed on a computer screen and specific areas can be enlarged or highlighted. If there is a suspicious area, your doctors can use the computer to take a closer look. The images also can be transmitted electronically from one location to another.

This study underscores earlier research showing that digital mammography is better at detecting breast cancer in women who:

  • are younger than 50
  • have dense breasts
  • are still menstruating or are perimenopausal (starting menopause), but have had a period within the previous 12 months

This study also suggests that digital mammography is better at finding breast cancer in women aged 60 to 69, as well as hormone-receptor-negative breast cancers.

Many imaging centers are now in the process of switching over from traditional film mammography to digital mammography. This is causing an increase in the number of women who are getting called back for additional testing. As radiologists get used to reading the digital images -- especially for a woman who has always had films done -- they may be more likely to call a woman back to take more views of potentially suspicious areas. Be aware of this if you make the switch from film mammography to digital mammography, and try not to worry prematurely if you get called back. As radiologists have more digital mammograms to compare to the latest one, it's likely that false positive rates will go down.

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 may want to 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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