Mammogram Readings Need to Be Seen in Perspective

One of the scariest things a woman can hear from her doctor is that there is a suspicious-looking mass on her mammogram. That news can shake a woman's sense of well-being even after further testing fails to find evidence of breast cancer.

Women should keep in mind that a mammogram is a screening test, not a diagnostic test, according to one of the authors of a recent study. In most cases further testing shows the masses to be non-cancerous, and in 10 percent of cases, radiologists misread normal tissue as abnormal.

"An 'abnormal' result cannot alone indicate cancer," says Mary B. Barton, M.D., M.P.P., assistant professor of ambulatory care and prevention at Harvard Medical School and Harvard Pilgrim Health Care in Boston and one of the co-authors of the study. She points out that doctors decide on diagnosis and treatment based on a biopsy, which is a sample of tissue used to look for cancer.

"On the other hand, women perceive mammograms to be highly accurate and thus are often alarmed by any abnormality," Barton says.

An abnormal mammogram indicates that further testing should be done, such as a diagnostic mammogram, ultrasound, or biopsy, and usually the abnormality is found not to be cancerous.

In addition to the probability that a breast mass is benign, there's also the possibility of a misreading of a mammogram by an unskilled or inexperienced radiologist.

Barton is one of the authors of a recent study published in the Journal of the National Cancer Institute, which found a significant number of false-positive readings of mammograms. The data was collected from 2,169 women, who were the source for 8,734 mammograms, which were then screened by 24 radiologists, from 1985 to 1993.

The researchers reported a correlation between a radiologist inaccurately reading a mammogram and his or her experience and training - the younger the doctor, the greater likelihood of a false-positive reading. Additionally, age and breast tissue characteristics of the patient are factors in the false-positive rate. Most women who have received false-positive readings are:

• Younger women whose breasts tend to be denser
• Women with a history of breast biopsies
• Family history of breast cancer
• Women who are taking hormone replacement therapy

What should women do?

"The one certain element in a woman's control at the present is to be sure that her current facility has her previous mammogram on hand for comparison - even if it was done elsewhere," Barton says.

Timing could also be important. She explains there is data to suggest that a mammogram done in the first 12 days of the menstrual cycle, for women who are still menstruating, may be more accurate due to differences in breast density through the menstrual cycle.

Hearing the news

"False-positive results can lead to additional diagnostic testing that can be quite costly," says Lisa M. Reisch, Ph.D., research consultant for the department of internal medicine at the University of Washington, Harborview Medical Center in Seattle, and another co-author of the study. She adds that for women whose evaluations go on to a biopsy, the small risk of infection and scars needs to be considered. "Perhaps more important than the physical and financial impact of false positive results is their direct impact on women's overall sense of well-being."

Women may find themselves feeling very confused when they find out they have had a false-positive mammogram reading. According to Barton, although some women are unaffected by the news of a false-positive reading, others may have heightened concerns about their own health or about their own risk of breast cancer for weeks or even months.

She adds that women can mention their feelings to their gynecologists and primary care physicians, if only to let them know what they have been going through.

Know the facts

According to Reisch, women should be aware that false-positive readings could occur. "It is our belief that both physicians and patients should have an accurate assessment of a patient's risk of breast cancer AND their risk of a false-positive mammogram reading. This is a very important point for future research and interventions," she says.

"It is possible that knowledge of the individualized risk information, for a false positive or a false negative, given to patients at the time of the mammogram may prove to be useful," Reisch says. The perception of risk related to the development of breast cancer, along with the possibility of having a false mammogram reading, are very important points for future intervention, she says.

Be prepared

Although there is no data to support that the same facility should be used for yearly mammograms, it is important to have previous mammogram films available so that any current findings can be compared to the prior films. Before your next scheduled mammogram, you can get copies of your prior films and send them to the new facility or bring them with you.

"Do not be shy about asking questions of your primary care physician or gynecologist who ordered your mammogram if you have any questions or uncertainty. If they don't know the answer themselves, they can find answers for you, and they may have some reassuring information that could help you feel better about the situation," Barton says.

Sources:

National Cancer Institute Web site. Cancer facts: screening mammograms: questions and answers. 2002. Accessed November 3, 2002.

Elmore JG, Miglioretti DL, Reisch LM, et al. Screening mammograms by community radiologists: variability in false-positive rates. J Natl Cancer Inst. 2002;94:1373-80.

This article was reviewed and updated June 2007.