Mammography screening ten years on: reflections on a decade since the 2001 review

Peter Gøtzsche, Director of the Nordic Cochrane Centre, is one of the authors of the landmark 2001 Cochrane systematic review ‘Screening for breast cancer with mammography’. Ten years on from first publication, he reflects on the review’s impact on healthcare policy and practice.

See also: Cochrane in the News report on planned review of UK breast cancer screening policy and the Cochrane Library Special Collection on breast cancer detection.

It created a lot of stir when we published our systematic review of mammography screening in The Lancet and in The Cochrane Library in October 2001. We showed that - because of substantial overdiagnosis – women who are screened have higher rates of aggressive treatment, including increased mastectomies. We also raised concerns about the reported benefits of screening based on our analysis of the methods used in several of the trials. In fact, we concluded in the Cochrane review that “The currently available reliable evidence has not shown a survival benefit of mass screening for breast cancer.”

Our finding of increased mastectomies has consistently been ignored by screening advocates for 10 years, and information from many cancer charities and governmental agencies continues to state the opposite – that screening decreases mastectomies - despite having no reliable data to support this claim. We recently confirmed that screening increases mastectomies, using data from both the Danish and Norwegian screening programmes (1, 2). We have also shown that many screening-detected cancers would have regressed spontaneously if they had been left alone, without treatment (3). By our estimates, the level of overdiagnosis in countries with organised screening programmes is about 50% (1).

Studies published in the last couple of years have failed to find an effect of screening in Europe, and have also failed to find a decrease in the occurrence of advanced cancers. When screening doesn’t decrease advanced cancers, it cannot work. We summarised the most important of this research in September 2011 (1).

There are likely three main reasons why screening is no longer effective. Adjuvant therapy, such as tamoxifen and chemotherapy, is highly effective (even when the cancer has metastasised), but was used very little in the old randomised trials. Increased breast cancer awareness has likely also been important, as women attend a doctor much earlier today if they have found anything unusual (1). Finally, diagnosis and treatment have been centralised in many countries, so that experts are available in all disciplines required for optimal processes.

Therefore, what was considered so controversial in 2001 is now increasingly being recognised to be true, even by people who advocated the introduction of screening in the first place. The tides are plainly turning for mammography screening, and it is now essential that women be provided with information that allows them to make an informed choice about mammographic screening, rather than being pushed toward mammography as routine, while being told it is an unambiguously beneficial test.

In 2009, we published an information leaflet on mammography screening in BMJ and on our website, www.cochrane.dk, which volunteers have translated into 11 languages. We clearly need to update the leaflet, which starts thus: “It may be reasonable to attend for breast cancer screening with mammography, but it may also be reasonable not to attend, as screening has both benefits and harms.” It is getting more and more difficult to argue that it is reasonable to attend for breast screening.

Peter C. Gøtzsche
Director, The Nordic Cochrane Centre
pcg@cochrane.dk
October 2011

References

1 Jørgensen KJ, Keen JD, Gøtzsche PC. Is mammographic screening justifiable considering its substantial overdiagnosis rate and minor effect on mortality? Radiology 2011;260:621-6.

2 Suhrke P, Mæhlen J, Schlichting E, Jørgensen KJ, Gøtzsche PC, Zahl PH. Effect of mammography screening on surgical treatment for breast cancer in Norway: comparative analysis of cancer registry data. BMJ 2011; 343:d4692. http://www.bmj.com/content/343/bmj.d4692.full

3 Zahl PH, Gøtzsche PC, Mæhlen J. Natural history of breast cancers detected in the Swedish mammography screening program; a cohort study. Lancet Oncol 2011;12 Oct. DOI:10.1016/S1470-2045(11)70250-9.