Volume 178 - Issue 4
Screening mammography and mortality
Author: Peter C Gøtzsche
Med J Aust 2003; 178 (4): 189-190. || doi: 10.5694/j.1326-5377.2003.tb05145.x
Published online: 17 February 2003
Published online: 17 February 2003
To the Editor: In a recent letter in the Journal,1 Rodger writes that breast screening is unlikely to affect overall mortality and notes that this "gives the lie to the conclusions of Olsen and Gøtzsche's overview, which are based only on overall mortality".
English is not my first language, but according to my English–English dictionary "give the lie to" means either "to disprove" or "to accuse of lying", and a related adjective is "mendacious". In actual fact, however, in our Cochrane Review,2 we carefully analysed both breast cancer mortality and all-cancer mortality. We found breast cancer mortality to be an unreliable outcome that is biased in favour of screening. For deaths ascribed to any cancer, including breast cancer, we found a relative risk of 1.02 (95% CI, 0.95–1.10) for the two trials with medium-quality data,3-5 and a relative risk of 1.00 (95% CI, 0.91–1.10) for the only trial with poor-quality data that reported all-cancer mortality.6 If it were true that screening reduced breast-cancer mortality by 30%, as some Swedish researchers have claimed,7 then the expected relative risk for all-cancer mortality should not be greater than 0.95. These findings should raise concern rather than complacency.
Another, recent indication that things are not what they purport to be is provided by the results of the large Two-County study. A Swedish overview of the randomised trials reported a 10% reduction (95% CI, 0.73–1.11; absolute reduction, 5.0/1000 to 4.5/1000) in breast-cancer mortality for one of the two counties,8 whereas the authors of the Two County study reported a 24% reduction (95% CI, 0.62–0.93; absolute reduction, 5.7/1000 to 4.3/1000),9 with the same type of statistics, within the same age group of women (40–74 years), and after a similar follow-up (1.2 v 1.3 million women-years).
The conclusion in our Cochrane Review is: "The currently available reliable evidence does not show a survival benefit of mass screening for breast cancer (and the evidence is inconclusive for breast cancer mortality)." I would not have expected Rodger, as an editor of the Cochrane Breast Cancer Group that approved and published our Cochrane Review, to talk about "giving the lie" to our results.
Competing interests
None identified. The views expressed are mine and are not necessarily the views or the official policy of the Cochrane Collaboration.
References
- Rodger A. Screening mammography and mortality [letter]. Med J Aust 2002; 177: 333.<eMJA full text>
- Olsen O, Gøtzsche PC. Screening for breast cancer with mammography (Cochrane Review). In: The Cochrane Library, Issue 4, 2001. Oxford: Update Software. i1082280
- Andersson I, Aspegren K, Janzon L, et al. Mammographic screening and mortality from breast cancer: the Malmo mammographic screening trial. BMJ 1988; 297: 943-948. i1082282
- Miller AB, To T, Baines CJ, Wall C. Canadian National Breast Screening Study–2: 13-year results of a randomized trial in women aged 50-59 years. J Natl Cancer Inst 2000; 92: 1490-1499.
- Miller AB, To T, Baines CJ, Wall C. The Canadian National Breast Screening Study: update on breast cancer mortality. J Natl Cancer Inst Monogr 1997; (22): 37-41. i1082285
- Tabar L, Fagerberg CJG, Day NE. The results of periodic one-view mammographic screening in Sweden. Part 2: Evaluation of the results. In: Day NE, Miller AB, editors. Screening for breast cancer. Toronto: Hans Huber, 1988: 39-44. i1082287
- Tabar L, Fagerberg CJ, Gad A, et al. Reduction in mortality from breast cancer after mass screening with mammography. Randomised trial from the Breast Cancer Screening Working Group of the Swedish National Board of Health and Welfare. Lancet 1985; 1: 829-832. i1082289
- Nyström L, Andersson I, Bjurstam N, et al. Long-term effects of mammography screening: updated overview of the Swedish randomised trials. Lancet 2002; 359: 909-919. i1082291
- Tabar L, Vitak B, Chen HH, et al. The Swedish Two-County Trial twenty years later. Updated mortality results and new insights from long-term follow-up. Radiol Clin North Am 2000; 38: 625-651. i1082293