How effective are breast cancer screening programmes by mammography? Review of the current evidence.

Randomised controlled trials showed that breast cancer screening by mammography reduces breast cancer mortality in women over age 50 by 25-30%. However, it was not clear if this effect would persist outside the controlled trial environment or even could be enhanced. We review the current evidence of the impact of long-standing breast cancer screening programmes (Australia, Canada, Denmark, Finland, Iceland, Italy, the Netherlands, Spain, Sweden and the United Kingdom) on breast cancer mortality. The decrease observed in women invited to screening ranges from 16% to 36%. Breast cancer mortality reductions range from 24% to 48% in women having attended at least one screen after correcting for selection bias. Although evaluation design, time period studied, participation rates achieved differ, the trend in mortality reduction is consistent. Adjuvant therapy is estimated to contribute about one third to this decrease. We conclude that mammography screening programmes implemented for at least 10 years achieve a similar, but not greater mortality reduction as the randomised controlled trials. However, it may take some more years before the full impact of these mammography screening programmes can be assessed.