TUESDAY, April 3 (HealthDay News) — Implementation of a mammography screening program leads to a substantial amount of overdiagnosis, according to a study published in the April 3 issue of the Annals of Internal Medicine.

To estimate the percentage of overdiagnosis of breast cancer that could be attributed to mammography screening, Mette Kalager, M.D., from the Harvard School of Public Health in Boston, and colleagues compared the incidence of invasive breast cancer from 1996 to 2005 in counties in Norway which did and did not implement a screening program. To account for temporal trends in the incidence of breast cancer, the incidence rates during the preceding decade were included. The cohort comprised 39,888 patients with invasive breast cancer, of whom 7,793 were diagnosed after the initiation of the screening program.

Using an approach calculated by accounting for the expected reduction in incidence following cessation of screening after age 69, the researchers found that the estimated rate of overdiagnosis attributable to the program was 18 to 25 percent. To account for average lead time, an approach which compared incidence in the current screening group with incidence among women two and five years older in historical screening groups estimated the rate of overdiagnosis at 15 to 20 percent. These estimated rates translated to six to 10 women overdiagnosed for every 2,500 women invited for screening.

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“Overdiagnosis and unnecessary treatment of nonfatal cancer creates a substantial ethical and clinical dilemma and may cast doubt on whether mammography screening programs should exist. This dilemma can be reduced only when potentially fatal cancer that requires early detection and treatment can be reliably identified,” the authors write.

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