By Mary Newell, MD and Peter R. Eby, MD FSBI, and the Breast Screening Leadership Group
While randomized controlled trials (RCT’s) are the most stringent way to assess whether a certain test of treatment decreases death from a disease, there are other data that can be used to further understand the effect of a test as well. Delivering screening mammograms to the community, i.e., service screening, provides an opportunity to evaluate the effect the test has on the general population when widely used by women.
After RCT’s showed that screening mammography saves lives, population-based national screening programs were put in place in the 1980s and 90s throughout the world. Screening mammography is now a routine part of health care in at least 26 countries (1). Data from many of these programs have been analyzed to see if they confirm the RCT results – that invitation to mammography screening, and more directly, exposure to mammography screening, decreases breast cancer deaths.
The results of cohort studies and case-control studies of service screening confirm the results of RCT’s: deaths from breast cancer decrease when widespread screening programs are introduced. In a case-control trial in Western Australia by Nickson and colleagues, death from breast cancer decreased by 52% among women choosing to be screened compared to women who did not (2). A meta-analysis (summary of many different studies) of Australian and European case-control trials showed that breast cancer deaths decreased by 49% in groups of women who used screening mammography compared to those who did not (2). A cohort study published by Coldman and associates reported that groups of women who participated in Canadian service screening programs had a 40% lower death rate from breast cancer than women who did not (3). A different analysis of cohort studies found that breast cancer deaths were reduced by 43% in populations of women who were screened with mammography (4).
Service studies demonstrate that the benefit of screening mammography in terms of lives saved is even higher than RCT’s indicated. This is in part because they measure the effect of screening on women who actually had mammograms, not just those who were invited to have a mammogram. Service screening studies also tend to measure the effect of more recent screening practices that have benefited from improved mammography technology, better breast positioning techniques, and improved interpretive skills. While RCT’s laid the foundation decades ago, data from recent studies of the effects of widespread screening programs confirm that mammograms save lives.
Data from Population Service Screening
Breast Cancer Screening Programs in 26 ICSN Countries, 2012: Organization, Policies, and Program Reach. U.S. National Institutes of Health International Cancer Screening Network website. http://appliedresearch.cancer.gov/icsn/breast/screening.html. Cited March15,2015
Nickson C, Mason KE, English DR, Kavanagh AM. Mammographic screening and breast cancer mortality: a case-control study and meta-analysis. Cancer Epidemiol Biomarkers Prev. 2012 Sep;21 (9):1479-88. PMID:22956730
Coldman A, Phillips N, Wilson C, et al. Pan-Canadian study of mammography screening and mortality from breast cancer. J Natl Cancer Inst. 2014 Oct 1;10(11). Print 2014 Nov. Erratum in: J Natl Cancer Inst. 2015 Jan’107(1). PMID:25274578
Gabe R, Duffy SW. Evaluation of service screening mammography in practice: the impact on breast cancer mortality. Ann Oncol. 2005;16 Suppl 2:153-62. Review. PMID: 15958448