Study Finds Mammogram Results Often Misinterpreted (dateline December 5, 2002)
A new study finds that physicians often misinterpret mammogram results at community clinics, causing women to undergo unnecessary worry and additional testing. However, the same study also shows that when women return to the same facility each year for their mammogram, the chances of a correct film reading increase. Furthermore, radiologists with several years of experience interpreting mammograms tend to make fewer errors when reading films compared to younger doctors. Mammography is still the most accurate method of detecting breast cancer, according to the researchers, and women should continue receiving the exam but with the knowledge that further testing may be needed to clarify the mammogram results.
Mammography is a special type of x-ray imaging used to create detailed images of the breast. The U.S. Food and Drug Administration reports that mammography can find 85% to 90% of breast cancers in women over age 50 and can discover a lump up to two years before it can be felt. The U.S. National Cancer Institute recommends that women 40 years of age and older receive mammograms every one to two years, and that women 50 years of age receive mammograms every year.
Despite being the current gold standard in breast cancer detection, mammography also been associated with "false positive" results; in other words, physicians sometimes believe they have found a cancer on a mammogram film when in fact, a woman is cancer-free. False positive mammogram results require additional diagnostic work-ups, with tests such as ultrasound, and may sometimes require tissue sample (biopsy) to confirm whether a woman has breast cancer.
To study the prevalence of false positive mammogram results in the community, Joann G. Elmore, MD, MPH, of the University of Washington School of Medicine, and her colleagues analyzed mammogram results that were interpreted by 24 radiologists who read 8,734 screening mammograms from 2,169 women. The mammograms were interpreted over an eight year period to allow for follow-up.
Dr. Elmore and her team found a significant range of false positive mammogram results among the radiologists: 2.6% to 15.9%. When the researchers factored in patient age, this rate dropped to 3.5% to 7.9%, since mammograms tend to be easier to interpret in older women who have less dense breast tissue.
Notably, the researchers found a significant reduction in interpretative errors (approximately 70%) when women returned to the same mammography facility each year. Returning to the same facility enables radiologists to compare a patients current mammogram to her previous ones, helping them make a more accurate interpretation based on observed breast tissue changes from year to year. The study also found that older radiologists with at least 15 years of field practice made fewer errors when interpreting mammograms than their younger peers.
The bottom line of the study: women should still undergo regular mammography because it is the most accurate tool to screen for breast cancer among women with no signs of the disease. However, women should also understand that mammography interpretation is not an exact science. While understandably stressful, women should be aware that a positive mammogram result does not necessarily mean that cancer is present. It simply means that further testing is needed to confirm or deny the existence of cancer. According to Dr. Elmore, a woman has a 50% chance of one false positive mammogram results over a period of 10 annual mammograms.
To increase the success of breast cancer screening, women 20 years of age and older should practice monthly breast-self exams to feel for lumps and other breast abnormalities. All women should also receive regular physician-performed clinical breast exams.