Mammography is good at finding breast cancer, especially among women ages 50 and older. However, it is most accurate when combined with a clinical breast exam. Among women ages 50 and older, between six and 27 percent of cancers may be missed with mammography alone, depending on several factors, including breast density [24-25]. When mammography is combined with clinical breast exam, about four percent more cancers are found than with mammography alone [26]. This improvement is even greater among women with dense breast tissue [26].
One downside of missing so few cancers is false positive results. These occur when a mammogram finds something that looks abnormal, but turns out to be benign. The more mammograms a woman has, the more likely she is to have a false positive result that will require more tests (more on follow-up tests). One large study found that the chance of having a false positive result after 10 mammograms was nearly 50 percent [27].
Thinking that a false positive result is breast cancer can cause fear and worry. However, this does not outweigh the life-saving value of regular screening. The most important job of mammography is to find as many cancers as possible, not to avoid false positive results.
Studies are looking at the impact that postmenopausal hormone use has on the accuracy of mammograms. Results from the Women's Health Initiative found that women who took estrogen plus progestin had breast cancers that were found at a more advanced stage than breast cancers found in women who did not take these hormones [28]. The women who took hormones also had increases in breast density and the number of abnormal mammograms (not explained by the higher breast density) that needed follow-up with further tests [28-31]. Exactly how, and if, these results may affect future screening guidelines is unclear. Learn more about risks linked to postmenopausal hormone use.
Experience matters
To get an accurate mammogram reading, you need a high quality image and a good interpretation of that image. One factor that may affect accuracy is the experience of the radiologist who reads the mammogram. Not all studies show high-volume mammography increases accuracy. However, radiologists who read a large number of mammograms each year are generally better able to interpret them than those who read fewer or those who do not read them routinely [32-34].
Seeking a high-volume mammography center may help you feel assured that your mammogram will be read correctly. However, lower-volume centers appear to be just as good at reading mammograms as higher-volume facilities [35]. 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 percentage of false positive results each year. The lower the false positive rate, the better the center or radiologist is at accurately reading mammograms. The Agency for Healthcare Research and Policy guidelines suggest a false positive rate of no more than 10 percent per year [36].
Updated 10/05/09
