Mammography for breast cancer screening
For over 20 years, there has been active discussion in the medical community about whether the benefits of mammography outweigh the risks.
This debate was sparked again when two Danish scientists reviewed the evidence on mammography. They concluded that many randomized controlled trials on mammography were too flawed to give good information. Using only the data from the remaining studies, they concluded mammograms did not lower a woman's chance of dying from breast cancer [47-48]. In the most recent update, one of the same researchers concluded (despite problems with certain studies) the evidence as a whole showed mammography likely reduces the risk of death from breast cancer .
The debate continued in 2009 with the release of the U.S. Preventive Services Task Force recommendations (learn more) .
Most major health organizations have concluded mammography saves lives. Although there may be some problems with certain studies, the evidence still shows mammography is a valuable screening tool.
Differences in screening recommendations for women ages 40 to 49
Mammography in women 40 to 49 saves lives, but the benefit is less than for older women.
Most major health organizations, including the American Cancer Society and the National Cancer Institute, have concluded that the modest survival benefits of mammography in women ages 40 to 49 outweigh the risks of false positive results and recommend yearly mammograms for women ages 40 to 49.
The U.S. Preventive Services Task Force meta-analysis of eight randomized controlled trials found mammography modestly reduced the risk of breast cancer mortality (death) in women 40 to 49 . This study found that to prevent one breast cancer death, 1,904 women 40 to 49 would need to be screened with mammography .
Weighing the benefits and risks, the Task Force does not recommend routine mammography for all women 40 to 49 . The Task Force encourages women 40 to 49 to talk to their health care providers and make informed decisions about when to start mammography screening . The American College of Physicians also recommends mammography decisions for a woman 40 to 49 be based on her breast cancer risk profile and her own preferences (after she weighs the potential benefits and harms of screening mammography with her provider) .
Over-treatment of ductal carcinoma in situ (DCIS)
There are valid concerns about the over-diagnosis and over-treatment of ductal carcinoma in situ (DCIS) with mammography screening. Since the introduction of mammography, the number of women diagnosed with DCIS has increased. In 2013, it is estimated that there will be about 55,000 new cases of DCIS .
Although DCIS is non-invasive, without treatment, the abnormal cells could become invasive breast cancer over time. Left untreated, it is estimated about 20 to 30 percent of low grade DCIS may progress to invasive breast cancer . Higher grade DCIS may be more likely to turn into invasive breast cancer if left untreated.
At this time, there is no way to tell which cases of DCIS will go on to invasive breast cancer and which will not. So, 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.
Because not all cases of DCIS will become invasive breast cancer, some women with DCIS may be "over-treated.” They get little benefit (beyond peace of mind) from treatment because they would never develop invasive breast cancer with or without treatment for DCIS.
Choosing the appropriate treatment for DCIS is a major research challenge. Researchers are studying ways to identify the cases of DCIS most likely to turn into invasive breast cancer. This would allow treatment to be targeted to those who are at higher risk. However, at this time, the standard of care is to treat each case of DCIS.
Read more from our Chief Scientific Advisor, Dr. Eric Winer, as he comments on the issue of mammography leading to over-diagnosis and over-treatment.
What does this mean for you?
Despite some ongoing debate, mammography is still the best 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.
Learn more about breast cancer screening recommendations for women at average risk.
Learn more about breast cancer screening recommendations for women at higher risk.