Limitations of Mammograms

Mammograms are the best breast cancer screening test we have at this time, but they have their limits. They can miss some cancers, and sometimes they can lead to extra tests and treatments that might not have been needed.

False-negative results

In some cases, mammograms might miss a breast cancer diagnosis. A false-negative mammogram looks normal even though breast cancer is present. False-negative mammograms can give people a false sense of security.

Overall, screening mammograms miss about 1 in 8 breast cancers. People with dense breasts are more likely to get false-negative results.

It’s important to see your doctor if you have new breast symptoms, even if you’ve had a normal screening mammogram recently. Additional tests such as a diagnostic mammogram or a breast ultrasound might be needed.

False-positive results

A false-positive mammogram looks abnormal even though there is no cancer in the breast.

About 1 in 10 screening mammograms are abnormal, sometimes requiring extra testing (diagnostic mammograms, ultrasound, MRI, or a breast biopsy) to find out if the change is cancer. In about 90% of cases, an abnormal finding on an initial mammogram is actually benign (not cancer).

Who is most likely to get a false-positive result?

False-positive results are more common in women who are younger, have dense breasts, have had breast biopsies, have breast cancer in the family, or are taking estrogen.

About half of the women getting annual mammograms over a 10-year period will have a false-positive finding at some point.

The odds of a false-positive finding are higher for the first mammogram or if previous mammograms aren't available for comparison. People who have past mammograms available for comparison reduce their odds of a false-positive finding by about half.

Potential risks

False-positive mammograms can cause anxiety. They can also lead to extra tests to be sure that cancer isn’t there, which cost time, money, and might cause physical discomfort.

Overdiagnosis and overtreatment

Finding cancers that would never cause problems is called overdiagnosis.

While screening mammograms can often find invasive breast cancers and ductal carcinomas in situ (DCIS) that need to be treated, it’s possible that some findings on mammograms would never grow or spread. These cancers are not life-threatening and never would have been found or treated if the person had not gotten a mammogram.

Overdiagnosis can lead to overtreatment, or getting treatment that’s not really needed.

Currently, experts have no way to tell which cancers will be life-threatening and which would never cause problems. Because of this, they advise treating all breast cancers. This exposes some women to the side effects of cancer treatment, even though it might not have been needed.

Overdiagnosis seems to be more common in older women, but the benefits of testing often outweigh this risk.

Pain or discomfort

The mammogram procedure can cause pain or discomfort, especially during compression of the breast for images. If possible, choosing a time when your breasts are less tender, such as after your menstrual cycle if you are still menstruating, might help.

Each image typically takes 10 to 15 seconds of compression. If you experience discomfort during the exam, let the examiner know. They might be able to reposition you or reduce the amount of compression while taking the images.

Radiation exposure

Because mammograms are x-ray tests, they expose the breasts to radiation. The amount of radiation from each mammogram is low, but it can still add up over time. To learn more, see Mammograms.

When mammograms might not be helpful

The value of a screening mammogram depends on a woman’s overall health. Finding cancer early might not help a person live longer if they have other serious or life-threatening health problems, such as heart, kidney, liver, or lung disease.

The American Cancer Society breast cancer screening guidelines emphasize that women with serious health problems or short life expectancies should discuss with their doctors whether they should continue having mammograms. Our guidelines also stress that age alone should not be the reason to stop having regular mammograms.

It’s important to know that even though mammograms can often find breast cancers that are too small to be felt, treating a small tumor does not always mean it can be cured. A fast-growing or aggressive cancer might have already spread, even if the tumor in the breast is still small.