A new analysis of deaths from breast cancer in Sweden before and since the establishment of county screening programs adds considerable support to the scientific evidence that regular breast cancer screening with mammography saves lives.
Writing in the journal Cancer, Duffy et al. report on their extensive evaluation of organized mammography screening services in seven Swedish counties that include more than 30% of the women in Sweden. The investigators looked at breast cancer mortality trends among women before and after mammography screening was introduced. Because of the completeness of Swedish medical records, the investigators were able to examine the number of women invited to be screened, identify who did and did not get mammograms, and examine information about each diagnosed case of breast cancer as to whether it was found in women who participated in screening or those who did not.
Among the screened women aged 40-69 in six of the counties and those aged 50-69 in the additional county, death from breast cancer was reduced 44 percent compared with rates in the pre-screening period.
Mortality rates for all women in the counties, i.e., women who participated in screening as well as women who were invited to the program who chose not to participate (non-compliers), were still 30 percent lower after screening was introduced than in pre-screening periods. Non-compliance ranged from eight percent to 30 percent in the invited population.
Counties with more than 10 years of screening had a combined mortality reduction of 32 percent, while those in which screening had been offered for 10 years or less had an 18 percent reduction in breast cancer mortality. The analysis included 2,044 breast cancer deaths from 14,092 cancers in the combined pre-screening and screening periods in the seven counties.
In an accompanying editorial, Stephen A. Feig, MD, a diagnostic radiologist from Mount Sinai Hospital in New York City, says that the Duffy study "confirms beyond any doubt" that the mortality reductions that were found in the large randomized clinical trials can be obtained in non-research screening services.
Feig adds that these service screening studies contribute to the body of evidence on the efficacy of early breast cancer detection, and can "effectively refute the controversial claims made in the last year by two Danish researchers (Lancet, January 8, 2000; Lancet, October 20, 2001) that randomized clinical trial results which demonstrate reduced breast cancer mortality were not valid."
The benefit of breast cancer screening has been well established by the world's randomized clinical trials," explained Robert A. Smith, Ph.D., a co-author of the study and director of cancer screening for the American Cancer Society.
"But it's very important to measure the effect of breast cancer screening now that it is part of health policy, and to determine the actual benefit for those women who participate in screening, since the experimental studies cannot do that. It's impressive that the results in these seven counties are remarkably similar. What is clear is that modern mammography is even more beneficial than we've previously estimated," Smith said.
SOURCES:
Cancer, August 1, 2002
American Cancer Society (http://www.cancer.org)
