The U.S. Preventive Services Task Force (USPSTF) published its findings on the efficacy of breast screening methods in reducing deaths from breast cancer in the Nov. 17, 2009, issue of "Annals of Internal Medicine." The task force reviewed eight studies conducted between 2001 and 2008 that were randomized, controlled trials with mortality outcomes and multiple data sources for screening effectiveness and harms. The review revealed that benefits of annual mammography as a routine practice for women younger than 50 and older than 74 are outweighed by potential harms caused by radiation. Exposure to radiation is currently the only known danger of mammograms. However, the limitations of mammography include risks due to false positive and false negative results.
Radiation
Mammograms expose women and their breasts to ionizing radiation, which is known to cause cancer and is cumulative over a woman's lifetime. Between the ages 60 and 69, the task force concluded that mammograms did prevent one cancer death per 377 women screened. After age 74, however, risks were found to outweigh the benefits again, and USPSTF advises that routine screening of these women should stop. The task force also recommended that women between the ages of 50 and 74 could maintain benefits and reduce harm by doubling the length of time between routine mammograms.
False Positives
The interpretation of mammograms by radiologists is a factor in their accuracy. One-third of women routinely screened over 10 years will have at least one false negative. Emotional stress and physical scarring from unnecessary biopsies can be burdensome.
The National Institutes of Health reported on its website the results of a 2007 study published in the "New England Journal of Medicine" that examined the results of computer-aided detection (CAD), which is frequently used to help radiologists spot cancers. For every cancer detected, 156 women underwent unnecessary tests. Many of the cancers that were detected were not life-threatening. Researchers in this study concluded that CAD reduces the accuracy of mammograms.
According the the National Cancer Institute, false positives occur more often in younger women as well as in those with a history of previous biopsies, those with a family history of breast cancer and women who are taking hormone replacement therapy.
False Negatives
The National Cancer Institute asserts that screening mammograms, those done to look for cancer in women who have no signs or symptoms of the disease, detect cancer when it is present about 80 percent of the time. However, up to 20 percent of women who receive negative results--meaning no cancer was found--actually do have breast cancer. Because of the prevalence of glandular tissue in the breasts of younger women, breast cancer can be more difficult to detect. The results of mammograms are more accurate for menopausal and post-menopausal women, whose breast tissue is less dense.
