Mammography is a screening test for breast cancer. It is 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.
This has caused ongoing debate over:
This debate has led to different recommendations on 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 .
Mammography benefits by age group
Risk of dying from breast cancer compared to women who did not get mammograms
Number of breast cancer deaths avoided per 10,000 women screened for 10 years
Women who got mammograms on a regular basis had the same risk of dying from breast cancer
Women who got mammograms on a regular basis had a 14 percent lower risk of dying from breast cancer
Women who got mammograms on a regular basis 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 two main risks of mammography screening.
Over-diagnosis occurs when a mammogram finds 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.
Some researchers estimate about 20-30 percent of DCIS and invasive breast cancers found with mammography may be over-diagnosed .
Even without treatment, these over-diagnosed breast cancers would never progress to invasive breast cancer and would never have caused problems.
Although DCIS is non-invasive, without treatment, the abnormal cells can sometimes become invasive over time.
Left untreated, findings from older studies estimate 40-50 percent of DCIS cases may progress to invasive breast cancer .
However, these estimates are based on old data (before mammography). Since the introduction of mammography in the 1980s, the number of women diagnosed with DCIS has increased a lot. So, the true risk of DCIS progressing to invasive breast cancer may be lower (fewer cases of DCIS may progress).
At this time, there is 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.
So for now, women with DCIS are treated with lumpectomy (also called breast conserving surgery) plus radiation therapy or mastectomy. Some women are also treated with hormone therapy.
Since not all cases of DCIS will become invasive breast cancer, some women with DCIS may be over-treated; meaning these women never would have developed invasive breast cancer, even without treatment.
Researchers are studying ways to identify the cases of DCIS most likely to become invasive breast cancer. This would allow treatment to be targeted to those who are at higher risk and might allow some people to avoid treatment.
Researchers are also studying whether some cases of DCIS with a lower risk profile can be treated less aggressively than they are treated now.
Learn more about DCIS.
Sometimes a mammogram can show 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 (may be called a diagnostic mammogram), breast ultrasound or breast MRI. Sometimes, a biopsy is needed. A biopsy removes some of the tissue in the breast to check for cancer.
Most abnormal findings on a mammogram are not breast cancer.
Understanding the chances of having a false positive result may help ease the fear and worry over an abnormal finding on a mammogram.
The table below shows estimates of outcomes for 10,000 women who get a mammogram.
For example, after one screening, 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 that mammography saves lives. However, we cannot say it saves 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 found early. They will get treatment and will not die from breast cancer.
For an individual woman who never develops breast cancer however, there may be no benefit from mammography, only risks.
The same is true of risks.
For example, a woman may get a false positive result on her mammogram and have an unnecessary biopsy. For any one woman, this may not be a big problem.
However, if thousands of women have unnecessary biopsies, this adds up to a lot of unneeded medical procedures, anxiety and cost.
In making screening guidelines, organizations have to look at the benefit 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.
Health organizations agree that women ages 50 and older should get mammograms. However, there is some debate over how often these women should get a mammogram.
Some health organizations recommend mammography every year for women 50 and older .
Other organizations recommend mammography every other year (every 2 years).
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 that mammography every 2 years gives almost as much benefit as mammography every year while reducing the 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 risk.
You are 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 [2-4].
Learn more about radiation exposure during a mammogram.
Despite some ongoing debate, mammography is still the most effective screening tool used today for the early detection of breast cancer.
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.
Discover the different ways you can help