Screening for breast cancer with mammography
Editorial Group: Cochrane Breast Cancer Group
Published Online: 19 JAN 2011
Assessed as up-to-date: 20 NOV 2008
Copyright © 2011 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
How to Cite
Gøtzsche PC, Nielsen M. Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2011, Issue 1. Art. No.: CD001877. DOI: 10.1002/14651858.CD001877.pub4.
- Publication Status: Edited (no change to conclusions)
- Published Online: 19 JAN 2011
A variety of estimates of the benefits and harms of mammographic screening for breast cancer have been published and national policies vary.
To assess the effect of screening for breast cancer with mammography on mortality and morbidity.
We searched PubMed (November 2008).
Randomised trials comparing mammographic screening with no mammographic screening.
Data collection and analysis
Both authors independently extracted data. Study authors were contacted for additional information.
Eight eligible trials were identified. We excluded a biased trial and included 600,000 women in the analyses. Three trials with adequate randomisation did not show a significant reduction in breast cancer mortality at 13 years (relative risk (RR) 0.90, 95% confidence interval (CI) 0.79 to 1.02); four trials with suboptimal randomisation showed a significant reduction in breast cancer mortality with an RR of 0.75 (95% CI 0.67 to 0.83). The RR for all seven trials combined was 0.81 (95% CI 0.74 to 0.87).
We found that breast cancer mortality was an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death. The trials with adequate randomisation did not find an effect of screening on cancer mortality, including breast cancer, after 10 years (RR 1.02, 95% CI 0.95 to 1.10) or on all-cause mortality after 13 years (RR 0.99, 95% CI 0.95 to 1.03).
Numbers of lumpectomies and mastectomies were significantly larger in the screened groups (RR 1.31, 95% CI 1.22 to 1.42) for the two adequately randomised trials that measured this outcome; the use of radiotherapy was similarly increased.
Screening is likely to reduce breast cancer mortality. As the effect was lowest in the adequately randomised trials, a reasonable estimate is a 15% reduction corresponding to an absolute risk reduction of 0.05%. Screening led to 30% overdiagnosis and overtreatment, or an absolute risk increase of 0.5%. This means that for every 2000 women invited for screening throughout 10 years, one will have her life prolonged and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress for many months because of false positive findings. It is thus not clear whether screening does more good than harm. To help ensure that the women are fully informed of both benefits and harms before they decide whether or not to attend screening, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk.
Plain language summary
Screening for breast cancer with mammography
Screening with mammography uses X-ray to try to find breast cancer before a lump can be felt. The goal is to treat cancer early, when a cure is more likely. The review includes seven trials that involved 600,000 women who were randomly assigned to receive screening mammograms or not. The review found that screening for breast cancer likely reduces breast cancer mortality, but the magnitude of the effect is uncertain. Screening will also result in some women getting a cancer diagnosis even though their cancer would not have led to death or sickness. Currently, it is not possible to tell which women these are, and they are therefore likely to have breasts or lumps removed and to receive radiotherapy unnecessarily. The review estimated that screening leads to a reduction in breast cancer mortality of 15% and to 30% overdiagnosis and overtreatment. This means that 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 will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress for many months because of false positive findings.
It is thus not clear whether screening does more good than harm. Women invited to screening should be fully informed of both the benefits and harms. To help ensure that the requirements for informed consent for women contemplating whether or not to attend a screening program can be met, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk.
8個符合資格之研究被確立。我們排除了有偏誤的試驗，並且分析涵括600,000女性資料。3項合適的隨機對照試驗顯示乳房攝影在降低乳癌13年死亡率上是不顯著的(RR: 0.90;95% I: 0.79 – 1.02)；4項次優的隨機對照試驗則表示乳房攝影能顯著的降低乳癌的死亡率(RR為 0.75, 95% CI: 0.67 to 0.83)。所有7個試驗的總RR為0.81(95% I: 0.74 to 0.87)。我們發現乳癌的死亡率來作為結果(outcome)較為不可靠，因為在篩檢的方式各有不同，產生偏誤。而最主要的原因是死因的誤判。較合適的幾項隨機對照試驗並沒有發現乳房攝影對於癌症死亡率有所改善，包括了乳癌10年後死亡率(R .02, 95% CI 0.95 to 1.10)及13年後的全死因死亡率(allcause mortality, RR: 0.99, 95% CI: 0.95 – 1.03)。 2個合適的隨機對照試驗測量了施行腫瘤切除術(lumpectomy)與全乳房切除手術(mastectomy)的數量，在有進行乳房攝影篩檢組別裡則有明顯的顯著差異(R .31, 95% CI 1.22 to 1.42)；而使用放射治療則似乎有所增加。
篩檢似乎可以降低乳癌的死亡率。在合適的隨機對照試驗中其效益是最低的，其合理估計死亡率15% 降低與絕對風險值降低0.05% 一致。乳房攝影篩檢導致30% 的過度診斷與過度治療，或者說讓絕對風險增加0.5% 。這代表著，每2000位女性接受乳房攝影篩檢10年，會有1位女性因為接受篩檢而延長壽命；而會有10位健康女性沒接受篩檢而無任何診斷，但將會接受不必要的治療。此外，將會有200多位婦女因為錯誤的陽性診斷而產生心理困擾。因此對於篩檢是否利大於弊尚未有清楚的答案。為了幫助女性在考慮進行篩檢前確定篩檢的利與弊，我們製作衛教單張讓民眾可以參考，此單張已翻譯成數種語言於以下網址www.cochrane.dk.
此翻譯計畫由臺灣國家衛生研究院(National Health Research Institutes, Taiwan)統籌。
在腫瘤可以觸摸出來之前，使用Xray乳房攝影嘗試找出腫塊。目的是為了在治癒可能性大的時候盡早治療癌症。整個回顧文獻包含了7項試驗，涵括共600,000隨機分派是否接受乳房攝影篩檢之婦女。本文獻指出乳房攝影篩檢似乎可以降低乳癌死亡率，但益處有多大仍無法確定。篩檢亦會導致一些癌症診斷，即便這癌症尚未產生生命危險或症狀。目前篩檢無法告訴婦女是否得到癌症，也因此婦女可能因此接受了不必要的乳房腫塊切除或是放射線治療。本回顧文獻預估篩檢可降低乳癌死亡率15% ，也導致了15% 的過度診斷及30% 的過度治療。這代表著，每2000位女性接受乳房攝影篩檢10年，會有1位女性因為接受篩檢而延長壽命。會有10位健康女性沒接受篩檢而無任何診斷，仍會接受不必要的治療。除此之外，超過200多位婦女會因為錯誤的陽性診斷而產生心理困擾數個月之久。 因此，對於篩檢的利與弊似乎尚未有明確的答案。在女性接受乳房篩檢時，應充分告知其利與弊。為了幫助女性充分了解接受或是不接受乳房攝影會有何影響，我們製作衛教單張讓民眾可以參考，此單張已翻譯成數種語言於以下網址www.cochrane.dk.