Weighing the Benefits and Risks of Screening Mammography
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 questions related to:
- How much benefit mammography offers
- The over-diagnosis and over-treatment of ductal carcinoma in situ (DCIS) and small, slow-growing invasive breast cancers
This has led to different recommendations for when to start getting screening mammograms and how often to have them.
Benefits of mammography
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 50 and older is much more common than breast cancer in women younger than 50 .
Benefits of mammography by age group
A meta-analysis of randomized controlled trials found:
Women who got mammograms may have had a lower risk of dying from breast cancer compared to women who did not get mammograms. However, the benefit was less than for older women.
Women who got mammograms had a 14 percent lower risk of dying from breast cancer compared to women who did not get mammograms.
Women who got mammograms had a 33 percent lower risk of dying from breast cancer compared to women who did not get mammograms.
Adapted from U.S. Preventive Services Task Force .
Getting regular screening mammograms lowers the risk of dying from breast cancer, but it doesn’t completely remove this risk.
Although the benefits of mammography are real, it’s not a perfect test. Some women who get regular mammograms may still be diagnosed with breast cancer and unfortunately, a small number of these women may still die from the disease.
Over-diagnosis and over-treatment
Over-diagnosis and over-treatment are the main risks of screening mammography.
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 [23,34,53-57,164]. 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 cause problems in a person’s lifetime.
Over-treatment occurs when a cancer that would have never caused symptoms or problems is found (over-diagnosis) and treated. This means even without treatment, the breast cancer would never have caused a problem. So, a person would be exposed to the risks of treatment, but get no benefit.
Over-treatment is a concern for those with 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, it’s estimated 40-50 percent of DCIS cases may progress to invasive breast cancer . In the same way, small, invasive breast cancers may grow over time.
Health care providers cannot predict which cases of DCIS will progress to invasive breast cancer and which cases will not. There’s also no way to tell which small, invasive breast cancers will progress if left untreated. So, all these breast cancers are treated.
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 of progressing, 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.
Other risks of mammography
False positives and follow-up tests
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 .
Learn more about follow-up after an abnormal mammogram.
What does this mean for you?
Despite some ongoing debate about the balance of benefits and risks, for most women, mammography is the most effective breast cancer screening test used today.
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.
Susan G. Komen® believes all women should have access to regular screening mammograms when they and their health care providers decide it is best based on their personal risk of breast cancer.
Learn about breast cancer screening recommendations for women at higher than average risk.
|For a summary of research studies on mammography in women ages 40-49, visit the Breast Cancer Research Studies section.|
|For a summary of research studies on mammography in women ages 50-69, visit the Breast Cancer Research Studies section.|
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Radiation exposure during a mammogram
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 [5-8].
Learn more about radiation exposure during a mammogram.