Perspectives
Cancer Environmental health
Volume 196 - Issue 1

Do the benefits of screening mammography outweigh the harms of overdiagnosis and unnecessary treatment?

Authors:  Robin J Bell and Robert C Burton

Med J Aust 2012; 196 (1): 17. || doi: 10.5694/mja11.11476
Published online: 16 January 2012
Download PDF (67 KB)
Share: Share on Blue Sky Share on Facebook Share on LinkedIn Share by email

No. Breast cancer researchers Robin Bell and Robert Burton believe that screening can result in overdiagnosis

Screening mammography undoubtedly saves lives. Since 1991, when Australia’s free national mammographic screening program (BreastScreen Australia) began, there has been a 29% reduction in breast cancer-specific mortality. However, our analysis of age-stratified data indicates that BreastScreen does not account for most of this mortality reduction.1 Furthermore, it is now recognised that the balance between the benefits and harms of screening has become increasingly unfavourable. Women should be given a balanced explanation of what BreastScreen offers them.

Our study analysed age-specific trends in breast cancer incidence, mortality and BreastScreen participation by Australian women aged 40–79 years since 1991.1 We found that the participation rates and relative mortality declines were the opposite of what the randomised controlled trials (RCTs) of mammographic screening had predicted. Women aged 40–49 years, who had the lowest BreastScreen participation (about 20%), had the largest mortality reduction (43.6%; 95% CI, 34.8%–51.2%). Women aged 60–69 years, who had the highest BreastScreen participation (about 60%), had the smallest mortality reduction (19.1%; 95% CI, 10.5%–26.9%). We also analysed the proportions of the declines in absolute breast cancer-specific mortality from 1991 to 2007 in two parts (before and after 1999–2000), to identify periods before and after any effect of BreastScreen on mortality might have been expected. We found that only about a third of the reduction in mortality in the age group invited for screening (50–69 years) occurred after 1999–2000.1

We have calculated the contribution that adjuvant endocrine therapy and chemotherapy could have made to the reduction in breast cancer mortality in Australia since 1991. Australia is unique in having six datasets from population-based breast cancer treatment surveys between 1986 and 1999. These document the stage at diagnosis and adjuvant treatment received for early breast cancer for different samples of Australian women. Based on a 10–15-year follow-up of their overviews of RCTs of adjuvant therapy in early breast cancer between 1985 and 2000, the Early Breast Cancer Trialists Collaborative Group (EBCTCG) concluded that appropriate use of anthracycline-based chemotherapy followed by tamoxifen for oestrogen-receptor-positive disease would result in annual breast cancer mortality reductions of 57% for oestrogen-receptor-positive women < 50 years of age and 45% for those aged 50–69 years.2 Our analysis, using 1999 Victorian survey results and the EBCTCG overview, found that breast cancer mortality reductions in Australian women in 1999 from adjuvant endocrine therapy and chemotherapy could have been up to 38% for women aged 40–49 years, and up to 24% for women aged ≥ 50 years.1 Therefore, adjuvant therapy had the potential to produce most of the 29% reduction in breast cancer mortality in Australia since 1991.

In theory, screening for an asymptomatic earlier stage of a disease that is more effectively treated with available therapies than symptomatic disease will produce less morbidity and mortality, but screening can result in overdiagnosis. Overdiagnosed breast cancers are those detected by screening mammography that would not have become symptomatic in the woman’s lifetime. Overdiagnosis by mammographic screening is most accurately estimated from the RCTs by comparing the increased numbers of breast cancers diagnosed in women invited to undergo screening compared with those not invited. A recent Cochrane systematic review of the RCTs puts the estimate at 30%.3 An estimate from incidence trends in New South Wales indicated that 30%–40% of invasive breast cancers were overdiagnosed in 1999–2001.4

The benefits and harms of mammographic screening are measured in terms of the ratio of lives saved to cases overdiagnosed. Using the RCT data, the 2011 Cochrane review determined that, with 30% overdiagnosis and a relative mortality reduction of 15%, “for every 2000 women invited for screening throughout 10 years, one will have her life prolonged. In addition, 10 healthy women, who would not have been diagnosed if there had not been screening, will be diagnosed as breast cancer patients and treated unnecessarily”.3 As the outcome of treatment for both symptomatic and asymptomatic disease improves, the impact of screening diminishes and the balance of benefits to harms will become less favourable. This has serious implications for health policymakers.

We believe it is time for women to be presented with a more balanced view about the benefits and harms of breast screening. Screening programs are currently undergoing review in the United Kingdom, and one of the first commitments is to a new process of developing written information for the public that will synthesise information on benefits and harms. There has been an assurance that the leaflet about breast cancer screening will be among the first to be revised.5

Authors

  • Robin J Bell PhD, MPH, FAFPHM1
  • Robert C Burton MD, PhD, FRACS2
  • 1. School of Public Health and Preventive Medicine, Monash University, Melbourne, VIC.

Correspondence: robin.bell@med.monash.edu.au

Competing interests

No relevant disclosures.

References

Provenance: Commissioned; not externally peer reviewed.

View this article on Wiley Online Library