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Previous studies have shown a 25% reduction in breast cancer mortality in Copenhagen following the introduction of mammography screening. A follow-up study was recently performed by the Nordic Cochrane Centre using an additional screening region and 5 years’ additional follow-up . Jørgensen and colleagues used Poisson regression analyses, adjusted for changes in age distribution, to compare the annual percentage change in breast cancer mortality in areas where screening was used with the percentage change in areas where it was not used, during the 10 years before screening was introduced and for the 10 years after screening was in practice (starting 5 years after the introduction of screening). The study was performed in Copenhagen, where mammography screening started in 1991, and Funen county, where screening was introduced in 1993. The rest of Denmark (about 80% of the population) served as an unscreened control group. The Cause of Death Register and Statistics in Denmark for 1971–2006 was used. Amongst women who could benefit from screening (ages 55–74 years), they found a mortality decline of 1% per year in the screening areas (relative risk (RR) 0.99, 95% confidence interval (CI) 0.96–1.01) during the 10-year period when screening could have had an effect (1997–2006). In women of the same age in the non-screened areas, there was a decline of 2% in mortality per year (RR 0.98, 95% CI 0.97–0.99) in the same 10-year period. In women who were too young to benefit from screening (ages 35–55 years), breast cancer mortality during 1997–2006 declined 5% per year (RR 0.95, CI 0.92–0.98) in the screened areas and 6% per year (RR 0.94, CI 0 .92–0.95) in the non-screened areas. For the older age groups (75–84 years), there was little change in breast cancer mortality over time in both screened and non-screened areas. Trends were less clear during the 10-year period before screening was introduced, with a possible increase in mortality in women aged less than 75 years in the non-screened regions. The authors concluded that they were unable to find an effect of the Danish screening programme on breast cancer mortality. The reductions in breast cancer mortality observed in screened regions were similar to or less than those in non-screened areas and in age groups too young to benefit from screening, and are more likely to be explained by changes in risk factors and improved treatment than by screening mammography.
Associate Professor of Reproductive Endocrinology, University of New South Wales; Director, Barbara Gross Research Unit, Royal Hospital for Women; Director, Sydney Menopause Centre, Royal Hospital for Women; Director, Womens Health and Research Institute of Australia, Sydney, Australia
Jørgensen KJ, Zahl PH, Gøtzsche PC. Breast cancer mortality in organised mammography screening in Denmark: comparative study. BMJ 2010;340:c1241. Published March 23, 2010.