How Doctors Interpret Mammograms

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Just like any other kind of interpretation, reading a mammogram is a skill that radiologists develop over time. They look for any signs of abnormality, including:

  • asymmetries (something on one side that's not on the other)
  • irregular areas of increased density
  • clusters of small calcifications
  • any area of skin thickening

But most of the time, a radiologist can't say for sure whether "it's cancer" or "it's not cancer" based on a mammogram alone, because both cancerous and non-cancerous growths can look the same. That's why, for many women, a mammogram is the first in a series of tests that will help reveal a bigger picture.

mammogram showing no discrete abnormalityMammogramLarger Version

You'll want to think beforehand about whether you want your mammogram films or digital images read immediately, while you wait, or at another time and place. Your doctor may want to read them first and discuss the results with you. Be sure you know where and when you'll find out what the films show BEFORE you get your mammogram. The main advantage of having them read immediately by the radiologist on site is that if the doctor sees anything suspicious, you can get more imaging done right away — close-up mammograms or an ultrasound. For more information, see our section on Getting Your Test Results.

Computer-aided detection and diagnosis

The radiologist also may use computer-aided detection and diagnosis, or CAD, to help zero in on any suspicious areas on the mammogram. If you had film-screen mammography, the doctor first would feed your films into a special machine that can convert them into digital images. If you had digital mammography, the images already are in digital format. The CAD software analyzes the images and any areas of concern are highlighted with markers on the screen. This can be useful in guiding the radiologist to check those areas more closely.

CAD was approved for use by the U.S. Food and Drug Administration in 1998, but whether or not it makes the interpretation of mammograms more accurate is unclear. According to the American Cancer Society, some studies have shown that CAD can help find cancers that doctors otherwise might have missed. However, it may be that having a second radiologist review the films is just as effective as using CAD.

In addition, there is some concern over “false positives” with CAD — that is, the technology may identify normal breast changes as potential cancers, leading to biopsies that aren’t really needed. One 2007 study published in the New England Journal of Medicine found that women who got screening mammograms at centers using CAD devices were more likely to be told their mammogram was abnormal and thus undergo a biopsy to rule out breast cancer. The study involved more than 220,000 women having mammograms during a 4-year period.

Right now, CAD systems are expensive and the technology is not yet widely used. Nevertheless, CAD is likely to become a more common tool as researchers continue to refine the technology and learn more about the best ways to use it.

If you’re interested in having CAD used to read your mammogram, talk with your doctor to see if it might be available.

Expert Quote

"Before you go to get a mammogram, make sure you know whether you're there for a screening mammogram or a diagnostic mammogram. If you're there for your annual screening mammogram, you may not meet with the radiologist or get your results the same day. Sometimes, there's an advantage to this. Getting your results later often means having two doctors look at your mammogram. A lump, pain, nipple discharge, breast implants, or breast surgery automatically make your mammogram diagnostic. If you have a lump, or other symptoms, tell the mammography center so they know what they're dealing with."

-- Susan Greenstein Orel, M.D.

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