Researchers Identify Factors that Increase Number of False-Positive Mammograms (dateline October 24, 2000)
Mammography is considered by physicians to be the gold standard in breast cancer detection, and currently, mammography is the only breast imaging exam approved by the U.S. Food and Drug Adminstration (FDA) to screen for breast cancer in women who show no signs or symptoms of the disease. Mammography can detect approximately 85% of breast cancers, often several years before a lump can be felt. While only approximately 7 of every 1,000 mammograms will lead to a breast cancer diagnosis, up to 100 of every 1,000 patients who have screening mammograms are referred for additional breast imaging. In a new study published in the Journal of the National Cancer Institute, researchers identify radiologic and patient variables that can contribute to a false-positive mammogram (mammogram results that falsely indicate cancer).
For the study, Cindy L. Christiansen, PhD of Boston University, and her colleagues, examined the medical records of 2227 women who were between 40 and 69 years of age on July 1, 1983 and who had had at least one previous screening mammogram. Each woman received nine mammograms over a 10-year period. Of the 9747 mammograms taken, 6.5% of the mammograms were false-positive and nearly one-fourth of the women in the study had at least one false-positive result. After nine years, the risk of having at least one false-positive mammogram was 43.1%.
The researchers then examined why some women were more likely to have false-positive mammograms than others. According to Dr. Christiansen and her colleagues, radiologic factors that increased a woman's chances of having a false-positive mammogram included the number of previous breast biopsies, having a family history of breast cancer, and current or past use of estrogen (in the form of oral contraceptives or hormone replacement therapy).
Other procedural factors that contributed to a higher risk of false-positive mammograms in the study included the time between mammograms (the longer the time, the higher the risk of a false-positive mammogram) and not having a previous mammogram to which the radiologist could compare the results of the current mammogram.
The age of the woman at the time of the mammogram was also a significant factor in the study. As a woman aged, the risk of having a false-positive mammogram decreased. This may be due to the fact that post-menopausal women tend to have less dense breast tissue than younger women. Breast density shows up as white regions on a mammogram film and may mimic breast cancer or other conditions. Additional mammographic views, other breast imaging tests (such as ultrasound), or biopsy may help rule out breast cancer in women with dense breasts.
The researchers also noted that the experience of the radiologist also influences the likelihood of false-positive mammograms. Among the 93 radiologists in the study, approximately half had false-positive rates of less than 5%. Approximately one fourth of the radiologists had false-positive rates between 5% and 10%, and another fourth of the radiologists had false-positive rates higher than 10%.
Factors That May Influence the Rate of False-Positive Mammogram Results
False-positive mammogram results usually require the patient to undergo additional breast imaging (with additional mammography views, ultrasound, or other imaging tests) or breast biopsy. While a false-positive mammogram result can cause unnecessary worry for the patient, mammography accurately detects approximately 85% of all breast cancers. The American Cancer Society believes that "the benefits of yearly mammography for women in their forties and older outweigh the impact of occasional false positive results leading to biopsy of non-cancerous abnormalities, and the economic cost of these examinations" (ACS).
The American Cancer Society, the American College of Radiology, the American College of Surgeons and the American Medical Association all recommend that women begin receiving annual mammograms at age 40.
Guidelines for the early detection of breast cancer:
- All women between 20 and 39 years of age should practice monthly breast self-exams and have a physician performed clinical breast exam at least every three years.
- All women 40 years of age and older should have annual screening mammograms, practice monthly breast self-exams, and have yearly clinical breast exams.
- Women with a family history of breast cancer or those who test positive for the BRCA1 (breast cancer gene 1) or BRCA2 (breast cancer gene 2) mutations may want to talk to their physicians about beginning annual screening mammograms earlier than age 40, as early as age 25 in some cases.
- The medical study, "Predicting the Cumulative Risk of False-Positive Mammograms," is published in the October 18, 2000 issue of the Journal of the National Cancer Institute ( Volume 92, Issue 20, 1657-1666). An abstract of the study is available at http://jnci.oupjournals.org/cgi/content/abstract/92/20/1657
- To learn more about the breast cancer diagnostic process, including statistics on the number of mammograms referred for additional imaging and the number of breast cancer diagnoses, please visit http://www.imaginis.com/breasthealth/diagnosis.asp
- To learn more about mammography, please visit http://www.imaginis.com/breasthealth/mammography.asp