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Researchers from Denmark have reported that breast cancer mammography screening initiated in 1991 reduced breast cancer mortality “without severe negative side effects for the participants.” The details of this report appeared in the January 15, 2005 issue of the British Medical Journal .

Breast cancer claims the lives of approximately 40,000 women annually in the United States alone. Cure rates for cancers that are detected and treated early are high with the use of standard treatment. However, cure rates are reduced dramatically in women whose breast cancer is detected and treated once it has spread to distant sites in the body. Therefore, screening for early breast cancer has become widespread with the use of mammography. However, over the past several years there have been publications that cast doubt on the ability of screening programs to reduce breast cancer mortality. There has also been criticism that screening leads to “over-diagnosis” of carcinoma in situ lesions that were not destined to spread and kill. These criticisms have led to a relatively large number of studies that have, in general, confirmed the effectiveness of screening mammography to detect early cancers and to prevent deaths. However, it must be pointed out that no randomized trial has clearly shown a survival benefit and most comparisons are between groups that are fortuitously unscreened and groups that are screened by invitation to participate in screening.

The current Danish study evaluated a large group of women in Copenhagen who were invited to participate in a screening program. This area of Denmark had a higher rate of breast cancer than other areas at the onset of the study. Most areas of Denmark were not offered screening and served as controls for this study. Women in the study were aged 50 years to 79 years, with the highest rate of breast cancer and breast cancer deaths occurring in the 75-79 year old group. Comparisons with concurrent unscreened populations and historical controls led to the conclusion that “Breast cancer mortality in the screening period was reduced 25% compared to what would be expected in the absence of screening”. When women who were invited to be screened but did not participate in screening were excluded, the reduction in breast cancer mortality was 37%.

These results add to a growing body of evidence that screening mammography saves lives. Women who are 40 years of age or older, or are at a high risk of developing breast cancer, may wish to speak with their physician about their individual risks and benefits of screening mammography.

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Reference: Olsen AH, Njor SH, Vejborg I, et al. Breast cancer mortality in Copenhagen after introduction of mammography screening:cohort study. British Medical Journal, doi:10.1136/bmj.38313.639236.82(published 13 January 2005)

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