For women at average risk, regular mammography is the primary screening test for breast cancer. Major medical organizations agree that screening beginning around age 40 can reduce the risk of dying from breast cancer, although they differ somewhat about how often mammograms should be performed and when routine screening should stop.
Women at higher-than-average risk—because of certain genetic mutations, a strong family history, previous chest radiation, or other factors—may need to begin screening earlier and may also benefit from breast MRI.
Dense breasts deserve special attention. Dense breast tissue is common. It both increases the risk of breast cancer and makes cancers more difficult to see on a mammogram. Women are now routinely informed whether their mammogram shows dense breasts.
Having dense breasts does not automatically mean that an ultrasound or MRI is necessary. The decision about additional screening should take into account overall breast cancer risk, degree of breast density, previous findings, and the potential benefits and drawbacks of additional testing.
The most useful screening plan is therefore not necessarily identical for every woman.
For women at average risk, there is broad agreement that mammography can detect breast cancer earlier, but there is real disagreement about exactly when routine screening should begin and how often it should be done.
U.S. Preventive Services Task Force (USPSTF): Mammography every two years from ages 40 through 74.
American Cancer Society (ACS): Women ages 40–44 have the option to begin annual mammograms; women 45–54 should have mammograms every year; at 55, women may switch to every two years or continue annually.
American College of Radiology: Recommends annual mammography beginning at age 40 for women at average risk.
But not everyone agrees that routine screening at 40 is the best choice for every woman. Some researchers and medical organizations emphasize that the absolute benefit of screening is smaller for women in their 40s, while false-positive mammograms, additional imaging, unnecessary biopsies, and overdiagnosis are more important concerns.
The American College of Physicians, for example, recommends that women ages 40–49 discuss the potential benefits and harms with their doctor and make an individual decision about whether to begin screening.
The disagreement is therefore not about whether mammography can find breast cancer. The question is when the benefits of finding cancers earlier outweigh the potential harms of screening.
For women in their 40s, family history, breast density, genetic risk, previous breast biopsies, and personal preferences can all be important in making that decision.
The strongest arguments for a less intensive approach to mammography are not arguments against screening. They focus on finding the best balance between the benefits of detecting important cancers early and the harms that screening can cause.
The benefit is real, but modest in absolute terms. Mammography reduces breast-cancer mortality across a screened population, but most women who are screened will not personally avoid a breast-cancer death because of screening. The potential benefit generally increases as the underlying risk of breast cancer increases.
Earlier screening comes with tradeoffs. Starting at 40 rather than 50 can prevent additional breast-cancer deaths, but it also results in substantially more false-positive mammograms, additional imaging, and biopsies.
Overdiagnosis is an important concern. Mammography sometimes detects cancers that would never have become a threat during a woman's lifetime. Because doctors cannot always know which cancers will progress, a diagnosis may lead to surgery, radiation, hormone therapy, or other treatment that ultimately would not have been necessary.
More frequent screening is not necessarily better. Annual screening can detect some cancers sooner, but it also produces more false positives and overdiagnosis. The USPSTF concluded that screening every two years provides a more favorable balance of benefits and harms than annual screening for women at average risk.
For women 75 and older, the uncertainty becomes greater. There is insufficient evidence to determine whether continued routine screening produces more benefit than harm. Overall health, life expectancy, previous screening history, and whether a woman would want treatment if cancer were found become particularly important.
The practical conclusion is that reasonable people can make different choices. Someone who places a very high value on finding a cancer as early as possible may prefer more frequent screening. Someone at relatively low risk who places greater weight on avoiding false positives, biopsies, and overtreatment may reasonably prefer a less intensive approach.
The debate is therefore not simply “mammograms or no mammograms.” It is about how much screening provides the best balance of benefit and harm for an individual woman.
There is no universally agreed age at which mammography should stop.
The USPSTF recommends screening through age 74 and concludes that there is not enough evidence to determine the benefits and harms of screening women age 75 and older.
The American Cancer Society takes a different approach. It recommends continuing mammography as long as a woman is in good health and has a life expectancy of at least 10 years.
This distinction is important. A healthy woman in her late 70s or 80s may have many years of life ahead of her and could potentially benefit from finding an important breast cancer early. For a woman with serious health problems or limited life expectancy, screening may be less likely to provide a meaningful benefit.
Rather than stopping automatically at a particular birthday, women over 74 may want to discuss overall health, life expectancy, personal breast cancer risk, and their own preferences with their healthcare provider.
Breasts are described as dense when they contain relatively more fibrous and glandular tissue and less fatty tissue. Breast density is determined from a mammogram—it cannot reliably be determined by how the breasts look or feel.
Dense breasts matter for two reasons. First, dense breast tissue can make a cancer more difficult to see on a mammogram, because both dense tissue and many cancers appear white. Second, women with dense breasts have a higher risk of developing breast cancer than women with mostly fatty breasts.
In the United States, mammography reports are now required to tell women whether their breasts are dense.
A natural question is whether women with dense breasts should routinely have another screening test, such as ultrasound or breast MRI, in addition to mammography. Additional imaging can find some cancers missed by mammography, but it can also produce more false-positive findings, additional testing, and unnecessary biopsies.
For women whose only additional risk factor is breast density, experts do not yet agree that everyone should routinely receive supplemental MRI or ultrasound. The decision may depend on the degree of breast density and the woman's overall breast cancer risk.
For women with dense breasts, a useful next step may therefore be to ask: “What is my overall breast cancer risk, and would additional screening be likely to benefit me?”
For women at average risk, mammography remains the standard screening test. Having dense breasts does not automatically mean that an MRI or ultrasound is needed.
Breast MRI is more sensitive than mammography and can detect cancers that mammograms miss. It is generally recommended in addition to mammography for women at high risk, such as some women with BRCA mutations, a very strong family history, or a calculated lifetime breast cancer risk of about 20% or greater. MRI can also produce more false-positive findings and usually requires an intravenous contrast agent.
Breast ultrasound can sometimes find cancers that are hidden by dense tissue on a mammogram. It does not require radiation or contrast. However, screening ultrasound also produces more false positives and additional biopsies, and it has not been established as a routine replacement for mammography.
For women with dense breasts who are not otherwise at high risk, the benefit of routinely adding MRI or ultrasound remains uncertain. The USPSTF has concluded that there is not yet enough evidence to recommend for or against supplemental MRI or ultrasound solely because a woman has dense breasts.
The most useful approach may be to consider breast density as one part of overall breast cancer risk. A woman with dense breasts plus other important risk factors may reach a different decision about additional screening than a woman whose only risk factor is breast density.
3D mammography, also called digital breast tomosynthesis, takes multiple X-ray images of the breast from different angles and combines them to create a more detailed view of the breast tissue.
Compared with traditional 2D mammography, 3D mammography generally finds somewhat more breast cancers and can reduce the number of women called back for additional imaging after a suspicious finding.
It may be particularly useful for women with dense breasts, because overlapping breast tissue can make abnormalities harder to see on a standard mammogram. However, even 3D mammography can miss cancers in very dense breasts.
The radiation exposure from modern 3D mammography is generally low, although the dose can vary depending on the equipment and whether separate 2D images are also taken.
For many women, 3D mammography has become a reasonable choice when it is readily available. But it does not eliminate the question of whether a woman at high risk might also benefit from screening with MRI.
Some women have a sufficiently high risk of breast cancer that mammography alone may not be enough.
Women at higher risk can include those who have:
A BRCA1 or BRCA2 mutation, or certain other inherited genetic mutations associated with breast cancer
A strong family history of breast or ovarian cancer
A calculated lifetime breast cancer risk of about 20% or greater
Previous radiation therapy to the chest at a young age, such as treatment for Hodgkin lymphoma
Certain high-risk findings from a previous breast biopsy
For women at high risk, screening may begin earlier than age 40 and often includes annual breast MRI in addition to mammography. The appropriate starting age depends on the particular risk factor.
Family history is especially important. Breast cancer in a mother, sister, or daughter, particularly at a young age, and multiple relatives with breast or ovarian cancer can indicate increased risk. Cancer history on the father's side of the family is just as important as the mother's side.
Women concerned about their family history can ask their healthcare provider about a formal breast cancer risk assessment. In some cases, genetic counseling and genetic testing may also be appropriate.
The important question is not simply “When should I start mammograms?” but “Am I at average risk or high risk?” The answer can substantially change the recommended screening plan.
What is my overall risk of developing breast cancer?
Do I have dense breasts, and how dense are they?
Should I have a 3D mammogram rather than a standard 2D mammogram?
Would an MRI or ultrasound provide a meaningful benefit for me?
Does my family history suggest that I should consider genetic counseling or testing?
How often should I have a mammogram?
At my age and with my overall health, should I continue mammography?
What are the possible benefits and harms of the screening plan you recommend?
Current recommendations on when to begin mammography, screening frequency, older women, and dense breasts.
A useful overview of mammography, screening benefits and harms, and screening for women at higher risk.
Explains breast density, how it affects breast cancer risk and mammography, and the questions surrounding supplemental screening.
Recommendations for women at average risk and women at high risk, including the use of breast MRI.
A thoughtful argument that women should be given clear information about both the benefits and harms of mammography so they can make an informed choice about when to begin screening.
A dissenting perspective on routine mammography that emphasizes the modest absolute mortality benefit, false positives, overdiagnosis and overtreatment, and the importance of informed individual choice. Updated July 2021.