Mammography is a screening test for breast cancer. It's used to find breast cancer early (before it causes any warning signs or symptoms), when the chances of survival are highest.
Regular mammography (along with follow-up tests and treatment if diagnosed) can reduce the chance of dying from breast cancer. However, the risks and benefits are not the same for all women.
There are still questions related to:
This has led to different recommendations for when to start getting screening mammograms and how often to have them.
The benefits of screening mammography vary by age. Women ages 50-69 get the most overall benefit for a number of reasons .
For example, breast cancer in women younger than 50 is much less common than breast cancer in women 50 and older .
Benefits of mammography by age group
Risk of dying from breast cancer for women who got mammograms on a regular basis (compared to women who did not)
Number of breast cancer deaths avoided per 10,000 women screened for 10 years
Women who got mammograms had a similar risk of dying from breast cancer
Women who got mammograms had a 14 percent lower risk of dying from breast cancer
Women who got mammograms had a 33 percent lower risk of dying from breast cancer
Adapted from U.S. Preventive Services Task Force, 2016 .
Getting regular screening mammograms lowers the risk of dying from breast cancer, but it doesn’t completely remove the risk.
Although the benefits of mammography are real, a woman who gets regular mammograms may still be diagnosed with breast cancer and unfortunately, may still die from the disease.
Over-diagnosis and over-treatment are the main risks of mammography screening.
Over-diagnosis occurs when a mammogram finds ductal carcinoma in situ (DCIS) or small, invasive breast cancers that would have never caused symptoms or problems if left untreated.
These breast cancers may never grow and some may even shrink on their own. Or, a person may die from another cause before breast cancer becomes a problem.
Studies suggest 5-50 percent of DCIS and small, invasive breast cancers found with mammography may be over-diagnosed [29-30,48-50]. A meta-analysis of 3 randomized controlled trials found over-diagnosis from mammography was 19 percent .
Even without treatment, these over-diagnosed breast cancers would never progress to invasive breast cancer and would never cause problems in a woman's lifetime.
Over-treatment occurs when a cancer that would have never caused symptoms or problems (if left untreated) is found (over-diagnosis) and treated. Even without treatment, the breast cancer would never have caused a problem.
Currently, it’s not possible to tell which breast cancers will never cause problems, so all breast cancers are treated. Over-treatment is a concern for those with ductal carcinoma in situ (DCIS) and some very early invasive cancers.
Although DCIS is non-invasive, without treatment, the abnormal cells can progress to invasive breast cancer over time. Left untreated, findings from older studies (before mammography was used) estimate 40-50 percent of DCIS cases may progress to invasive breast cancer .
In the same way, small, invasive breast cancers may grow over time.
Since the introduction of mammography in the 1980s, the number of women diagnosed with DCIS has greatly increased. So, the true risk of DCIS progressing to invasive breast cancer may be lower (fewer cases of DCIS may progress).
At this time, there’s no way to tell which cases of DCIS will become invasive breast cancer and which will not. However, higher grade DCIS may be more likely than lower grade DCIS to progress if left untreated .
There’s also no way to tell which small, invasive breast cancers will progress if left untreated.
For now, women with DCIS or a small, invasive breast cancer are treated with a lumpectomy plus radiation therapy or a mastectomy. With either surgery, hormone therapy may also be needed. Some women with small, invasive breast cancer may also get chemotherapy.
Since not all cases of DCIS and small, invasive breast cancer will progress, some women may be over-treated.
Researchers are studying ways to identify which cases of DCIS and small, invasive breast cancer are most likely to progress. This would allow treatment to be targeted to those who are at higher than average risk and might allow some people to avoid treatment.
Researchers are also studying whether some cases with lower risk profiles can be treated less aggressively than they are treated now.
Learn more about DCIS.
Sometimes a mammogram shows something abnormal that might be cancer, but turns out not to be cancer. This is called a false positive result.
If your mammogram shows something abnormal, you will need follow-up tests to check whether or not the finding is breast cancer.
These tests may include a follow-up mammogram (diagnostic mammogram), breast ultrasound or breast MRI. Sometimes, a biopsy is needed. A biopsy removes a small amount of tissue in the breast to check for cancer.
If you have an abnormal finding on a mammogram, try not to panic or worry. Most abnormal findings are not breast cancer. Understanding the chances of having a false positive result on a mammogram may help ease fear and worry over an abnormal finding.
The table below shows estimates of outcomes per 10,000 women who get a mammogram.
For example, after one screening, it's estimated 1,212 out of 10,000 women ages 40-49 will have a false positive result . Among older women, there are fewer false positive results .
Risks of screening mammography per 10,000 women (estimates for a single screening)
False positive result(false alarm)
Need a biopsy
False negative result(missed cancer)
The benefits and risks of mammography for the population can differ from those for an individual woman.
At the population level, we can say mammography saves lives by lowering the risk of dying from breast cancer. However, it doesn't save the life of every woman who gets screened. Not all women get the same benefit from mammography.
For example, say a large group of women get regular mammograms. Some of the women in the group will have a breast cancer that's found early. They will get treatment and will not die from breast cancer.
However, for an individual woman who never develops breast cancer there may be no benefit from regular mammogram screening, only risks.
Sometimes a result on a mammogram leads to a biopsy that shows no cancer. For any one woman, this biopsy may not be a big problem as the results were negative for breast cancer. However, if thousands of women have biopsies that don’t show cancer, this adds up to a lot of extra medical procedures, anxiety and cost.
In making screening guidelines, organizations look at the benefits and risks for a population of women rather than the benefits and risks for any one woman. They try to give recommendations that give the most benefit with the least amount of risk to the population.
These benefits and risks may be different for an individual woman though. Some women will get more benefits than the population as a whole and some will get more risks.
Despite some ongoing debate about the balance of benefits and harms, mammography is the most effective breast cancer screening tool used today for most women.
While any health decision is a personal one that involves weighing benefits and risks, most health organizations recommend women get mammograms on a regular basis.
Figure 3.1 shows breast cancer screening recommendations for women at average risk.
Learn about breast cancer screening recommendations for women at higher than average risk.
Mammography in women ages 40-49 may save lives, but the benefit is less than for older women. Individual study findings vary [8,23].
Some health organizations have concluded the modest potential benefits of mammography for women in their 40s outweigh the risks of false positive results, over-diagnosis and over-treatment [3-4].
Some health organizations recommend informed decision-making with a health care provider, guided by a woman's breast cancer risk profile [2-3].
If you are in your 40s, talk with your provider about when to start mammography screening.
Learn more about breast cancer screening recommendations for women ages 40-49.
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Health organizations agree women ages 50-69 (and at least some women 70 and older) should get mammograms. However, there’s some debate about how often these women should get a mammogram.
Some health organizations recommend mammography every year for women 50-69 (and for women 70 and older who are in good health) .
Other organizations recommend mammography every other year (every 2 years) [2-3].
For example, the U.S. Preventive Services Task Force recommends mammography every 2 years starting at age 50 . And, the American Cancer Society recommends mammography every 2 years starting at age 55 .
The Task Force reviewed the scientific evidence and concluded mammography every 2 years gives almost as much benefit as mammography every year while reducing risks .
Lifetime risks and benefits of screening mammography per 1,000 women ages 50-74
Mammographyevery other year
Fewer breast cancer deaths
False positive results (false alarms)
Unnecessary breast biopsy
Learn more about breast cancer screening recommendations for women at average risk.
Learn more about breast cancer screening recommendations for women at higher than average risk.
You're exposed to a small amount of radiation during a mammogram.
While the radiation exposure during mammography can increase the risk of breast cancer over time, this increase in risk is very small [5-7].
Learn more about radiation exposure during a mammogram.
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