Cancer Research UK & UCL Cancer Trials Centre, University College London, London, UK
Received 12 July; accepted 3 April 2003
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Abstract |
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Key words: breast cancer, mammography, review, screening
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Introduction |
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The effect of screening on breast cancer mortality |
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Two trials from Canada [10] were not included in the main analysis because they were not designed to investigate mammography alone and there was no unscreened control group. One trial was based on women aged 4049 years and compared annual mammography plus physician examination with an initial physician examination. The other, based on women aged 5059 years, compared annual mammography plus physician examination with annual physician examination.
All the trials showed a reduction in mortality. There is no evidence of heterogeneity (test for heterogeneity, P value 0.98) between the estimates, suggesting that the results were consistent with each other. This is reassuring, because the results came from different trials in different countries. Table 1 gives some details of the trials. In women aged 4074 years there is a statistically significant 22% reduction in breast cancer mortality (95% CI 1330). This is an underestimate, because not all women accepted the offer of screening in the trials (78% accepted). The estimated reduction in mortality is 28% assuming 100% uptake.
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There is a non-statistically significant reduction of 15% (relative risk 0.85, 95% CI 0.681.08), with no evidence of heterogeneity between the estimates (P value 0.84). If the Canadian trial [10] is included the pooled estimate is 7% (relative risk 0.93, 95% CI 0.761.15).
When the EUSOMA report was published (1993) several of the trials were still in progress. Since then the results have been updated, but they do not differ materially from those published previously; the effect on the meta-analyses would therefore be small. In the overview of the four Swedish trials the relative risk of breast cancer mortality was 0.77 (95% CI 0.670.88) in 1993 [1] and 0.79 (95% CI 0.700.89) in 2002 [11]. In the trial from Edinburgh the relative risk was 0.85 (95% CI 0.651.12) in 1993 [1] and 0.87 (95% CI 0.701.06) in 1999 [12]. It is reassuring that the effect of mammography has remained consistent even after a longer follow-up in the trials.
The trials clearly show that periodic mammography reduces the risk of dying from breast cancer. Although analysing the data according to age (4049 and 5074 years) is somewhat arbitrary, there is a suggestion that screening women <50 years old may be less effective. The data from such women are, however, relatively sparse and so no firm conclusions could be made.
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Translation of research results into practice and performance indicators |
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Adverse effects of screening |
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Screening process risks
Three psychological and physical factors were identified: (i) the anxiety associated with being invited for screening; (ii) the discomfort and pain associated with the examination itself (due to compression of the breast); and (iii) the risk of cancer induced by radiation exposure from mammography. There was little or no evidence to suggest that these were significant factors.
False-positive results
A woman with a false-positive result does not have breast cancer but has an abnormal mammogram and so is referred for further investigation. This will be associated with anxiety, particularly during the time between referral and when she is informed that she does not have breast cancer. Some of these women will also be referred for a biopsy, from which there will be further psychological morbidity, and pre-operative counselling may be required.
Overdiagnosis
Overdiagnosis, in this context, is the detection of slow-growing non-lethal breast cancer. Such women will unnecessarily undergo screening, diagnosis and treatment. A related problem is when screening identifies cancers whose prognosis is unaltered (because it is already metastatic, or because it could be curable if left until symptoms develop). Such women live with the knowledge that they have cancer for longer than would otherwise be the case if they were not screened.
Although there were concerns over the adverse effects of screening, studies at that time have shown them to be infrequent or relatively minor. They are, however, a reason for implementing and maintaining quality assurance measures in screening programmes.
Conclusions and recommendations
Regular mammographic examination, followed by diagnosis and treatment (as required) leads to a significant 22% reduction in breast cancer mortality.
Screening women aged 50 years should be part of organised public health programmes with full quality control and monitoring.
There is uncertainty over the effect of screening in women aged <50 years. If such women request it they should have it performed but after being informed of the uncertainty and the possible consequences. The main research need specified in the EUSOMA report was to adequately assess the value of screening in this age group to resolve the issue.
The benefits of screening demonstrated by the trials can be translated into practice, but with appropriate quality assurance. Several performance indicators of recognised value were specified that could be used successfully on a national basis. The adverse effects of screening should be recognised.
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Footnotes |
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References |
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2. Shapiro S, Venet W, Strax P, Venet L. Periodic Screening for Breast Cancer: The Health Insurance Plan Project and its Sequelae, 196386. London: Johns Hopkins University Press 1988.
3. Aron JL, Prorok PC. An analysis of the mortality effect in a breast cancer screening study. Int J Epidemiol 1986; 15: 3643.[Abstract]
4. Roberts MM, Alexander FE, Anderson TJ et al. Edinburgh trial of screening for breast cancer: mortality at 7 years. Lancet 1990; 335: 241246.[ISI][Medline]
5. Tabar L, Fagerberg G, Duffy SW, Day NE. The Swedish two-county trial of mammographic screening for breast cancer: recent results and calculation of benefit. J Epidemiol Community Health 1989; 43: 107112.[Abstract]
6. Tabar L, Fagerberg G, Duffy SW et al. Update of the Swedish 2-county program of mammography screening for breast cancer. Radiol Clin North Am 1992; 30: 187210.[ISI][Medline]
7. Andersson I, Aspegren K, Janzon L et al. Mammographic screening and mortality from breast cancer: the Malmö mammographic screening trial. BMJ 1988; 297: 943948.[ISI][Medline]
8. Frisell J, Eklund G, Hellstrom L et al. Randomised study of mammography screeningpreliminary report on mortality in the Stockholm trial. Breast Cancer Res Treat 1991; 18: 4956.[ISI][Medline]
9. Nystrom L, Rutqvist LE, Stig W et al. Breast cancer screening with mammography: an overview of Swedish randomised trials. Lancet 1993; 341: 973978.[ISI][Medline]
10. Miller AB, Baines CJ, To T, Wall C. Canadian National Breast Screening Study. Can Med Assoc J 1992; 147: 14591488.[Abstract]
11. Nystrom L, Andersson I, Bjurstam N et al. Long-term effects of mammography screening: updated overview of the Swedish randomised trials. Lancet 2002; 359: 909919.[CrossRef][ISI][Medline]
12. Alexander FE, Anderson TJ, Brown HK et al. 14 years follow-up from the Edinburgh randomised trial of breast cancer screening. Lancet 1999; 353: 19031908.[CrossRef][ISI][Medline]