Limitations of Mammograms

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: 

  • A false-negative mammogram looks normal even though breast cancer is present.
  • A false-positive mammogram looks abnormal even though there’s no cancer in the breast.

False-negative results

A false-negative mammogram looks normal even though breast cancer is present. Overall, screening mammograms do not find about 1 in 5 breast cancers.

  • Women with dense breasts have more false-negative results. 
  • Breasts often become less dense as women age, so false negatives are more common in younger women.
  • False-negative mammograms can give women a false sense of security, thinking that they don’t have breast cancer when in fact they do.

False-positive results

A false-positive mammogram looks abnormal even though no cancer is actually present. Abnormal mammograms require extra testing (diagnostic mammograms, ultrasound, and sometimes MRI or even a breast biopsy) to find out if the change is cancer.

  • 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.
  • The odds of a false-positive finding are highest for the first mammogram. Women who have past mammograms available for comparison reduce their odds of a false-positive finding by about 50%.
  • False-positive mammograms can cause anxiety. They can also lead to extra tests to be sure cancer isn’t there, which cost time and money and maybe even physical discomfort.

Mammograms might not be helpful for all women

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 disease, or severe 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.

Overdiagnosis and overtreatment

Screening mammograms can 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 and treating 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 don’t know which women fall into this group when the cancer is found because they can’t tell which cancers will be life-threatening and which won’t ever cause problems. Because of this, all cases are treated. This exposes some women to the adverse effects of cancer treatment that’s really not needed.

Still, overdiagnosis is not thought to happen that 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%.

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. For more on this, see Mammogram Basics.
 

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Hubbard RA, Kerlikowske K, Flowers CI, et al. Cumulative probability of false-positive recall or biopsy recommendation after 10 years of screening mammography: A cohort study. Ann Intern Med 2011;155:481-492.

Lauby-Secretan B, Scoccianti C, Loomis D, et al. Breast-cancer screening--viewpoint of the IARC Working Group. N Engl J Med. 2015;372(24):2353-2358.

Lee CI, Elmore JG. Chapter 10: Breast Cancer Screening. In: Harris JR, Lippman ME, Morrow M, Osborne CK, eds. Diseases of the Breast. 5th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2014.

Puliti D, Duffey SW, Miccinesi G, et al. Overdiagnosis in mammographic screening for breast cancer in Europe: A literature review. J Med Screen, 2012;19:Suppl 1:42-56.

Rosenberg RD, Hunt WC, Williamson MR, et al. Effects of age, breast density, ethnicity, and estrogen replacement therapy on screening mammographic sensitivity and cancer stage at diagnosis: Review of 183,134 screening mammograms in Albuquerque, New Mexico. Radiology 1998; 209:511–518. 

Last Medical Review: September 1, 2017 Last Revised: October 9, 2017

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