Mammography is a screening test for breast cancer. It’s used to find breast cancer early (before it causes and 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 on:
- 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 on 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 younger than 50 is much less common than breast cancer in women 50 and older.
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
Over-diagnosis and over-treatment are two main risks of mammography screening.
Over-diagnosis
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.
Studies suggest anywhere from 5 to 50 percent of DCIS and small, invasive breast cancers found with mammography may be over-diagnosed. 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 have caused problems.
Over-treatment
Although DCIS is non-invasive, without treatment, the abnormal cells can sometimes become invasive over time. In the small way, small, invasive breast cancers may grow over time.
Left untreated, findings from older studies (before mammography) estimate 40-50 percent of DCIS cases may progress to invasive breast cancer.
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.
How often should women aged 50 and older get a mammogram?
Health organizations agree women aged 50-69 (and at least come women 70 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 50-69 (and for women 70 and older who are in good health).
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 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 the risks.
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