Letters

Office of NHS cancer screening programme misrepresents Nordic work in breast screening row

EDITORIn Mayor's news story in the issue of 27 October the office of the NHS cancer screening programme in the United Kingdom misrepresents our research entirely.¹ The office says that our findings of more aggressive treatment of breast cancer among screened women are based on only two studies, classified as poor quality. They are not. Numbers of mastectomies as well as numbers of tumourectomies increase when women are screened. This finding is consistent and is based on all four of the seven screening trials that have published data on this, including the two medium quality trials from Canada and Malmö.²

The office also incorrectly notes that we did not investigate whether more aggressive treatment was beneficial since we published extensive mortality data. ^{2 3} Furthermore, it is wrong to say that our conclusion about the lack of benefit of mammography comes from an analysis of the two trials of medium quality. Our results for overall mortality and for deaths ascribed to any cancer, including breast cancer, are consistent and relate to both medium quality and poor quality trials. There was not even a trend towards a reduction in all cause mortality or all cancer mortality.

The office notes that many researchers would classify all seven studies as of similar quality. This statement is astonishing. We have shown important differences in quality and that the trials from Edinburgh and New York are flawed. For this reason, the editors from the Cochrane Breast Cancer Group suggested that we omitted the results from these two studies from our analyses, to which we agreed. There is now ample evidence from four large studies that lack of proper quality assessment of the individual trials in systematic reviews leads to grossly exaggerated claims of benefit.⁴

Accordingly, we have shown that the estimate for mortality from breast cancer in the poor quality trials is much lower and significantly different from the estimate based on the medium quality trials. ^{2 3} To disregard this finding is bad science. If anybody disagrees with our assessments of quality, we would like to know exactly on what grounds. However, to avoid more misquotations, we recommend our critics read our full report first (available at http://image.thelancet.com/lancet/extra/fullreport.pdf).

When the office claims that there is clear evidence of the benefit for mammography when all seven studies are combined, it overlooks not only that some studies are flawed but also the finding that mortality from breast cancer is a misleading and biased outcome measure that favours screening, as we and others have documented. ^{2 3 5}

Thus, all the statements offered by the office of the NHS cancer screening programme are misleading and misrepresent our research. This is depressing. It is a disservice to women's need for honest information, and it also underlines the importance of Richard Horton's statement in his commentary that "The implications for women and policy makers are substantial and require careful reflection and discussion."⁶ To crown it all, the statements are anonymous attacks on scientific work. This is improper and unfair since there is no accountability. Who gave these statements?

Peter C Gøtzsche, director. 
Nordic Cochrane Centre, Rigshospitalet, DK-2100 Copenhagen ø, Denmark pcg{at}cochrane.dk

Competing interests: None declared.

1.	Mayor S. Row over breast cancer screening shows that scientists bring "some subjectivity into their work." BMJ 2001; 323: 956[Free Full Text]. (27 October.)
2.	Olsen O, Gøtzsche PC. Cochrane review on screening for breast cancer with mammography. Lancet 2001; 358: 1340-1342[CrossRef][Medline].
3.	Olsen O, Gøtzsche PC. Screening for breast cancer with mammography. Cochrane Database Syst Rev 2001;(4): CD001877.
4.	Jüni P, Altman DG, Egger M. Systematic reviews in health care: Assessing the quality of controlled clinical trials. BMJ 2001; 323: 42-46[Free Full Text]. (7 July.)
5.	Early Breast Cancer Trialists' Collaborative Group. Favourable and unfavourable effects on longterm survival of radiotherapy for early breast cancer: an overview of the randomised trials. Lancet 2000; 355: 1757-1770[CrossRef][Medline].
6.	Horton R. Screening mammographyan overview revisited. Lancet 2001; 358: 1284-1285[CrossRef][Medline].