Contrary to recommendations from institutions urging women to undergo regular mammograms, screening mammography may increase survival rates by only negligible amounts, according to a recent study conducted by Norwegian researchers and published in the New England Journal of Medicine.
Despite vocal criticism from some in the health care and policy field, Dartmouth Medical School professor of community and family medicine H. Gilbert Welch wrote in an editorial also published in the New England Journal of Medicine that the study’s results make evident that screening mammography is not one of the most important, or vital, services of modern medicine. The health risks posed by unnecessary treatment due to overdiagnosis may not be balanced by the limited decrease in mortality associated with screening, he wrote.
The technique is subject to false positive results and needless treatment, and its low level of efficiency means that 2,500 women would have to be screened for 10 years in order to avoid one cancer-related death, according to Welch.
Researchers — who focused on women between the ages of 50 and 69 — compared the death rates of a group of women who were screened every two years with those of a group who did not undergo screening, the study reported. They also compared historical groups of women from a period spanning from 1986 through 1995.
As compared with the historical screening group, the death rate for those women who had access to screening mammography was reduced by 7.2 deaths per 100,000 individuals, according to the study. The fall in the death rate for the nonscreening group was 4.8 deaths per 100,000 women.
These results suggest that the screening mammography may only reduce breast cancer mortality rates by approximately 10 percent, a number much lower than scientists had anticipated, Welch wrote in his editorial.
“That physicians are still debating the relative merits of screening mammography despite the wealth of data suggests that the test is surely a close call, a delicate balance between modest benefit and modest harm,” Welch wrote.
Because the Norwegian study monitored a combination of screening mammography and the availability of multidisciplinary medical teams, the actual reduction in mortality rates due to screening alone may be as low as 2 percent, according to Welch. This estimate is significantly lower than that of the U.S. Preventive Services Task Force, which presents a figure between 15 and 23 percent.
“The accuracy of mammography for different age groups is sometimes related to the different composition in the breast and age-related changes in the breast,” Steven Poplack, clinical radiologist at Dartmouth-Hitchcock Medical Center, said in an interview. “For example, the proportion of fibroglandular tissue in the breast is higher for younger women. Since breast cancer usually is seen as a white object, it becomes more difficult to detect on a dense, white background.” In his editorial, Welch also outlined some potential issues with the study. The observational nature of the data and the fact that the subjects in the study may have contributed data to each group at different ages were potential sources of error, he wrote. The short follow-up time established by the researchers may also have been insufficient to monitor the effects of screening mammography fully.
In addition, the efficiency of screening mammography may have decreased over time as women have access to new means of early detection and evaluation, according to Welch.
Overall, however, widespread campaigns by organizations such as the American Cancer Society overstate the importance and effectiveness of regular mammograms, according to the editorial.
“The perception is largely the product of well-crafted public health messaging,” he wrote. “Given current data, such messaging must become more balanced.”
Mammography uses X-rays to project portions of the human breast in a two dimensional image onto a screen, according to the study. The resulting image does not take into account the three-dimensional nature of human anatomy, forcing doctors to detect abnormalities of the breast — such as early indicators of cancer — from an inexact picture.
The lack of clarity about the benefits associated with mammography suggests that women must be properly informed of downsides and capable of making their own decisions, without undue influence from physicians, according to Welch.
“No one can argue that screening mammography is one of the most important services we provide in medicine,” Welch wrote. “The time has come for it to stop being used as an indicator of the quality of our health care system.”