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Mammograms are the best breast cancer screening tests we have at this time. But mammograms have their limits. For example, they aren’t 100% accurate in showing if a woman has breast cancer. They can miss some cancers, and sometimes they find things that turn out not to be cancer (but that still need further testing to be sure).
A false-negative mammogram looks normal even though breast cancer is present. Overall, screening mammograms miss about 1 in 8 breast cancers.
A false-positive mammogram looks abnormal even though there is no cancer in the breast. Abnormal mammograms often require extra testing (diagnostic mammograms, ultrasound, and sometimes MRI or even a breast biopsy) to find out if the change is cancer.
The value of a screening mammogram depends on a woman’s overall health. Finding breast cancer early may not help her live longer if she has other serious or life-threatening health problems, such as serious 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.
Screening mammograms can often find invasive breast cancer and ductal carcinoma in situ (DCIS, cancer cells in the lining of breast ducts) that need to be treated. But it’s possible that some of the invasive cancers and DCIS found on mammograms would never grow or spread. (Finding cancers that would never cause problems is called overdiagnosis.) These cancers are not life-threatening, and never would have been found or treated if the woman had not gotten a mammogram. The problem is that doctors can’t tell these cancers from those that will grow and spread.
Overdiagnosis leads to some women getting treatment that’s not really needed (overtreatment), because the cancer never would have caused any problems. Doctors can’t always tell which cancers could 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 wasn't really needed.
Still, overdiagnosis isn't thought to happen very often. There’s a wide range of estimates of the percentage of breast cancers that might be overdiagnosed by mammography, but the most credible estimates range from 1% to 10%.
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. For more on this, see Mammogram Basics.
The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.
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on October 1, 2021.
Last Revised: January 14, 2022
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