MONDAY, Nov. 24 (HealthDay News) -- The cumulative incidence of breast cancer among women screened every two years is higher than that among women screened once after six years, implying that screening detects some invasive breast cancers that would naturally regress on their own, researchers report in the Nov. 24 issue of the Archives of Internal Medicine.
Per-Henrik Zahl, M.D., Ph.D., of the Norwegian Institute of Public Health in Oslo, Norway, and colleagues analyzed data on cumulative breast cancer incidence in age-matched cohorts of women before and after biennial mammography was introduced. Women who underwent all three mammograms during the 1996 to 2001 screening period comprised the screened group, while the control group was made up of women who would have qualified for screening had a program been instituted from 1992 through 1997, and who underwent a one-time prevalence screen.
Once the controls underwent prevalence screening, the screened group had a 22 percent higher prevalence, at 1,909 per 100,000 population versus 1,564 per 100,000, the data revealed.
"Our findings are equally consistent with the possibility that mammography either leads to a reduction in breast cancer mortality or has no effect at all," the authors write. "Our findings simply 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."
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