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These findings "provide new insight on what is arguably the major harm associated with mammographic screening, namely, the detection and treatment of cancers that would otherwise regress," Dr H. Gilbert Welch, from the Department of Veteran Affairs Medical Center, White River Junction, Vermont, and colleagues state.
The study, which is published in the Archives of Internal Medicine, involved 119 472 women, from 50 to 64 years of age, who underwent three rounds of mammography screening from 1996 to 2001 as part of the Norwegian Breast Cancer Screening Program. The cancer rates in this group were compared with those in 109 784 control women who would have been screened had the program been in place in 1992.
Women in the control group were invited to undergo a one-time screen at the conclusion of their observation period, the authors explain.
What the research found
As anticipated, the four-year cumulative incidence of invasive breast cancer in the screened group was higher than in the control group before screening: 1268 versus 810 cases per 100 000 population.
However, even after the one-time screen in the control group, the six-year cumulative incidence of breast cancer in the screened group was still higher: 1909 versus 1564 cases per 100 000 population.
"Because the cumulative incidence among controls never reached that of the screened group, it appears that some breast cancers detected by repeated mammographic screening would not persist to be detectable by a single mammogram at the end of six years," Welch and colleagues conclude.
"If the 'spontaneous remission' hypothesis is credible, it should cause a major reevaluation in the approach to breast cancer research and treatment," Dr Robert M. Kaplan, from University of California, Los Angeles, and Dr Franz Porzsolt, from the University of Ulm, Germany, write in a related editorial. "Certainly it is worthy of further evaluation. But, finding better data to assess the hypothesis will be difficult." – (Reuters Health, November 2008)
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