High-quality evidence from randomized trials demonstrated the efficacy of mammography in reducing breast cancer mortality by a significant 20% among 50-69 year old women invited to screening. However, there is a huge variability in the protocol, implementation strategies and quality of mammography screening across the globe. Among the 28 European Union (EU) countries, 23 reported to have implemented or planned population-based mammography screening in 2017, though the age at screening initiation (as early as 40 years) or to stop screening (extended to 74 years) and the screening interval (1-3 years) differed across the countries. Population-based screening programme in Australia invites women for mammography every two years, though 40-49 year old women can also participate. The Canadian Task Force on Preventive Health Care recommends mammography every 2-3 years between 50-69 years. The United States Preventive Service Task Force prioritizes biennial screening of women aged 50-74 years.
An evaluation of the key performance indicators reported great variability in screen-positivity (1.4% to 8.4%), detection rate of breast cancer (2.2/1000 to 5.8/1000) and breast cancer to DCIS ratio (3.3 to 12.1) among women undergoing prevalent screen in the EU. Reduction in breast cancer mortality among those participating in organized screening ranged between 33% and 43% in north Europe, 43% and 45% in south Europe and 12% and 58% in west Europe.
The balance between benefits and harms of mammography is intensely debated. A cohort study from Australia claims that mammography screening didn’t downstage the disease; rather rational use of hormonal-therapy and adjuvant chemotherapy accounted for the entire mortality reduction reported across the country between 1994 and 2013. An independent review panel commissioned by the Department of Health, England estimated that for every 10,000 women invited for screening at age 50, about 43 deaths from breast cancer would be prevented and for each breast cancer death prevented, about 3 over-diagnosed cases will be treated. This probably is a more realistic assessment.