Mammography is good at finding breast cancer, especially in women ages 50 and older. Overall, the sensitivity of mammography is about 78 percent [29-30]. This means mammography correctly identifies about 78 percent of women who truly have breast cancer. Among women over 50, sensitivity is about 83 percent [29-30].
False positive results
One downside of missing so few cancers is false positive results. These occur when a mammogram finds something that looks like cancer, but turns out to be benign (not cancer). The more mammograms a woman has, the more likely she is to have a false positive result that will require follow-up tests. Studies have shown the chances of having a false positive result after 10 yearly mammograms are about 50 to 60 percent [31-32].
Getting a false positive result can cause fear and worry . However, this does not outweigh the benefit of mammography for most women. The goal of mammography is to find as many cancers as possible, not to avoid false positive results.
Postmenopausal hormone use and mammogram findings
Some women take postmenopausal hormones (also known as menopausal hormone therapy or hormone replacement therapy) to relieve menopausal symptoms. However, the use of postmenopausal hormones increases breast cancer risk (learn more) . So, although postmenopausal hormone use is approved for the short-term relief of menopausal symptoms, the U.S. Food and Drug Administration (FDA) recommends women use only the lowest dose that eases symptoms for the shortest time needed .
Studies are looking at how postmenopausal hormone use affects the accuracy of mammograms. There are two main types of postmenopausal hormones used today: estrogen plus progestin and estrogen alone (learn more). Results from the Women's Health Initiative showed women who took estrogen plus progestin (but not women who took estrogen alone) had breast cancers found at a more advanced stage than breast cancers found in women who did not take these hormones [36-37]. Women who took either type of postmenopausal hormones had higher breast density and more abnormal mammograms (not explained by the higher breast density) that needed follow-up testing [36-40]. Exactly how, and if, these results may affect future screening guidelines is unclear.
Learn more about postmenopausal hormone use and breast cancer risk.
To get an accurate mammogram reading, you need a high quality image and a good reading of that image. The training and experience of the radiologist who reads the mammogram may improve his/her ability to interpret the image. Radiologists who read a lot of mammograms each year are generally better able to interpret them compared to those who read fewer or those who do not read them routinely [41-44].
Seeking a high-volume mammography center may help you feel assured your mammogram will be read correctly, but a lower-volume center may be just as good at reading mammograms . Most lower-volume, certified mammography centers provide good quality screening.
One way to assess the quality of a mammography center or radiologist is by the percent of false positive results each year (it may be hard to get this information though). The lower the false positive rate, the better the center or radiologist is at accurately reading mammograms. The Agency for Healthcare Research and Quality guidelines suggest a false positive rate of no more than 10 percent per year .
Can mammography miss breast cancer?
Although mammography is the best screening tool for breast cancer today, it is not perfect. Mammography misses about 17 percent of breast cancers . Depending on certain factors (such as breast density) mammography alone may miss up to 30 percent of breast cancers [29-30].
Combining mammography with clinical breast exam may improve its ability to find cancer. One study showed mammography plus clinical breast exam found about four percent more cancers than mammography alone . This improvement was even greater among women with dense breast tissue .
Learn more about clinical breast exam.