In the “real-world”, the reduction in breast cancer deaths associated with screening is small and not significant from a statistical standpoint, a study shows.
Nonetheless, “I’m encouraging everyone to continue with current recommendations,” said lead investigator Dr. Joanne G. Elmore. Women should have screening mammography every 1 or 2 years starting at age 40, according to the US Preventive Services Task Force.
Elmore, at the University of Washington in Seattle, and her colleagues analyzed data on women enrolled in six large healthcare plans in five states. They included 1351 women ages 40 to 65 years with a breast cancer diagnosis between 1983 and 1993, and who died of breast cancer between 1983 and 1998, along with a comparison group of 2501 women matched for age and risk level who were free of cancer.
The premise of the researcher’s study was that if screening prevents breast cancer deaths, those who died of the disease would have undergone less screening than the comparison group.
During the 3 years prior to the first suspicion of breast disease, there were 702 screening mammographies and 1853 screening clinical breast examinations among the women with cancer; corresponding numbers for comparison subjects were 1281 and 3288, the team reports in the Journal of the National Cancer Institute.
Overall, the researchers calculate, breast cancer screening compared with no screening was not associated with a significant reduction in breast cancer deaths.
These findings differ from those from clinical trials, in which screening was associated with a mortality benefit, Elmore pointed out.
“It’s possible that the quality of screening in the community may be different from expert trials in academic centers,” she suggested.
Another potential reason for the difference may be that “cancer treatments are improving survival regardless of the screening history,” she continued. “Or it may be that when a woman notices an abnormality, she is seeking medical attention much sooner now than 20 or 30 years ago, which also helps to reduce mortality.”
Regardless of the reasons for the lack of benefit seen in the current study, it should not change recommendations for breast cancer screening, Dr. Russell Harris, from the University of North Carolina at Chapel Hill, indicates in a related editorial. However, he adds, “It is time to emphasize research on the effectiveness of screening as currently practiced in the community.”
SOURCE: Journal of the National Cancer Institute, July 20, 2005.
Revision date: June 21, 2011
Last revised: by David A. Scott, M.D.