One million women develop breast cancer each year world-wide. Early detection and treatment are considered the most promising approach to reduce breast cancer mortality.
The first screening trial of mammography was initiated in 1963. Since then studies have been carried out in different countries. Most have reported reductions in breast cancer mortality and several countries have now established breast cancer screening programmes. The consensus on the value of mammography screening has recently been challenged by Danish investigators associated with the Cochrane Collaboration. They argued that many of the studies were scientifically flawed and concluded that there was no overall benefit from mammography.
The available evidence on breast cancer screening was evaluated in Lyon by a Working Group convened by the International Agency for Research on Cancer (IARC) of the World Health Organisation (WHO), from 5-12 March 2002. The group, consisting of 24 experts from 11 countries, concluded that trials have provided sufficient evidence for the efficacy of mammography screening of women between 50 and 69 years. The reduction in mortality from breast cancer among women who chose to participate in screening programmes was estimated to be about 35%. For women aged 40-49 years, there is only limited evidence for a reduction. The quality of the trials that were used to make these evaluations was carefully assessed. The working group found that many of the earlier criticisms were unsubstantiated, and the remaining deficiencies were judged not to invalidate the trials findings.
The effectiveness of national screening programmes varies due to differences in coverage of the female population, quality of mammography, treatment and other factors. Organised screening programmes are more effective in reducing the rate of death from breast cancer than sporadic screening of selected groups of women.
The working group also concluded that there is insufficient evidence that clinical breast examination or self-examination reduce mortality from breast cancer.