Drs. Lydia Pace and Nancy Keating of Boston s Brigham and Women s Hospital examined data from studies on mammography, especially the most recent ones. Because breast cancer is the second most common cause of cancer death in American women, and guidelines for mammography use have been changing, they reviewed the data on mammography benefits and harms. Their results were published in JAMA, and cogently reviewed in the Washington Post.
Examining all studies going back to 1960 the researchers determined that for 10,000 women aged 40-49 years receiving regular mammograms, 5 lives would be saved; for those aged 50-59, 10 lives would be saved; for those aged 50-59, 42 lives would be saved. Such results aren t unexpected, as for most women breast cancer is most likely to occur at older ages.
At the same time, Pace and Keating found that the potential harms of regular mammograms are not insignificant. The risk of a false positive result, that is finding an abnormality that turns out to be an artifact (that is, nothing at all) or a lesion that turns out not to be cancer, is over 60 percent for women aged 50 who have mammograms annually for 10 years. Such false positives can result in unnecessary radiation, surgery, or chemotherapy. The researchers noted that such risks increase when screening begins at earlier ages or is repeated annually.
Another potential harm from mammography is overdiagnosis, that is finding and treating a cancer that would not have affected the woman s long-term health. This could be because the cancer itself was indolent, or because the woman had co-existing health issues that were more life-threatening. The data on overdiagnosis were quite variable, however. Estimates ranged from 5 to 50 percent, because of differences in populations, study assumptions, and measurement methods.
The authors strongly supported the concept of informed decision-making, rather than following strict guidelines according to a patient s age. In their discussion they note, Informed decisions require reconciling information about the risks and benefits of screening with a patient s values. In addition, they acknowledged a woman s personal risk profile, for example family history, must be incorporated into the decision process.
ACSH s medical director, Dr. Gilbert Ross commented, The results of this study and Drs. Pace and Keating s interpretation make a great deal of sense. Hopefully organizations which publish mammogram guidelines will take note of these results and help save a lot of anxiety and unnecessary invasive treatments for a substantial number of American women.