Breast cancer mortality in Copenhagen after introduction of mammograph
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《英国医生杂志》
1 Institute of Public Health, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark, 2 University Hospital Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen ?, Denmark, 3 Mammography Screening Clinic, University Hospital Odense, Kl?verv?nget 10, DK-5000 Odense, Denmark
Correspondence to: A H Olsen a.h.olsen@pubhealth.ku.dk
Abstract
In the overview of five randomised trials from Sweden, a reduction of 29% was found in breast cancer mortality in women aged 50-69 at randomisation after a follow up of 5-13 years.1 Organised, population based, mammography service screening was introduced on the basis of these results in Copenhagen, the capital of Denmark, in 1991.2 Since then the validity of the trial results and the justification of mammography screening have been debated intensively.3 4 Furthermore, the adaptation of trial results to routine health care is not straightforward. Examining whether the screening programmes actually reduce mortality due to breast cancer is therefore important.
In Denmark, mammography screening was introduced in only three out of 16 administrative regions. The regions without a mammography screening programme thereby provide a natural control group during the full period of follow up. In addition, opportunistic screening has been limited.5 Taking advantage of this "natural experiment," and using the nationwide population and health registers in Denmark, we developed a method to determine the effect of mammography service screening on breast cancer mortality.6 We present here the results of the first 10 years of screening in Copenhagen.
Methods
For the period before screening started, Copenhagen had a significantly higher mortality due to breast cancer than the rest of Denmark (relative risk 1.22, 95% confidence interval 1.10 to 1.35), although there was some variation by age group. This had changed in the screening period, where Copenhagen had a lower breast cancer mortality than the rest of Denmark (0.91, 0.80 to 1.05). When we compared Copenhagen in the screening period with the period before screening, the relative risk was significantly lower than 1 (0.80, 0.68 to 0.94). When we compared the rest of Denmark in the screening period with the period before screening, the relative risk was 1.05 (0.99 to 1.11), again with some variation by age group. When we estimated the effect of the combination of invitation to screening and the interaction term between period and region adjusted for age, period, and region, the relative risk was 0.75 (0.63 to 0.89; table 2).
Table 2 Effect estimates for breast cancer mortality in the Copenhagen mammography screening programme
We estimated the cumulative effect of the combination of invitation to screening and the interaction term between period and region by year of follow up and adjusted for age at entry, period, and region (fig 2). Significance was reached after six years of follow up.
Fig 2 Estimated effect on breast cancer mortality of invitation to mammography screening in Copenhagen, cumulated over years of follow up
For the participants the estimated effect of combining participation in screening and the interaction term between period and region adjusted for age, period, and region resulted in a relative risk of 0.60 (0.49 to 0.74). On the other hand, women invited to screening who did not participate had a relative risk of 1.15 (0.91 to 1.46). On this basis, we estimated that in a situation without screening, participants would be a selected part of the population, with a relative risk of 0.95 compared with the total population. When we adjusted for this selection bias, the relative risk for the participants was 0.63.
When we used the same method as in the breast cancer mortality analysis, the invited population had a total cancer mortality (excluding breast cancer) close to that expected without screening (relative risk 0.96, 0.91 to 1.01).
Discussion
Nystr?m L, Rutqvist LE, Wall S, Lindgren A, Lindqvist M, Ryden S, et al. Breast cancer screening with mammography: overview of Swedish randomised trials. Lancet 1993;341: 973-8.
Mammography screening evaluation group, H:S Copenhagen Hospital Corporation. Mammography screening for breast cancer in Copenhagen April 1991-March 1997. APMIS 1998;106(suppl 83): 1-44.
G?tzsche PC, Olsen O. Is screening for breast cancer with mammography justifiable? Lancet 2000;355: 131-6.
Olsen O, G?tzsche PC. Cochrane review on screening for breast cancer with mammography. Lancet 2001;358: 1340-2.
Olsen AH, Jensen A, Njor SH, Villadsen E, Schwartz W, Vejborg I, et al. Breast cancer incidence after the start of mammography screening in Denmark. Br J Cancer 2003;88: 362-5.
Olsen AH, Njor SH, Vejborg I, Schwartz W, Dalgaard P, Jensen M-B et al. A model for determining the effect of mammography service screening. Acta Oncologica 2005 (in press).
Vejborg I, Olsen AH, Jensen M-B, Rank F, Tange UB, Lynge E. Early outcome of mammography screening in Copenhagen 1991-99. J Med Screen 2002;9: 115-9.
Fischerman K, Mouridsen HT. Danish Breast Cancer Cooperative Group (DBCG). Structure and results of the organisation. Acta Oncologica 1988;27: 593-6.
Andreasen AH, Mouridsen HT, Andersen KW, Lynge E, Madsen M, Olesen KP. Improved prognosis of breast cancer. Ugeskr L?ger 1994;156: 6512-7.
Andreasen AH, Andersen KW, Madsen M, Mouridsen H, Olesen KB, Lynge E. Regional trends in breast cancer incidence and mortality in Denmark prior to mammographic screening. Br J Cancer 1994;70: 133-7.
Blanks RG, Moss SM, McGahan CE, Quinn MJ, Babb PJ. Effect of NHS breast screening programme on mortality from breast cancer in England and Wales, 1990-8: comparison of observed with predicted mortality. BMJ 2000;321: 665-9.
Otto SJ, Fracheboud J, Looman CWN, Broeders MJM, Boer R, Hendriks JHCL, et al. Initiation of population-based mammography screening in Dutch municipalities and effect on breast-cancer mortality: a systematic review. Lancet 2003;361: 1411-17.
Jonsson H, Nystr?m L, T?rnberg S, Lenner P. Service screening with mammography of women aged 50-69 years in Sweden: effects on mortality from breast cancer. J Med Screen 2001;8: 152-60.
Duffy SW, Tabar L, Chen HH, Holmqvist M, Yen MF, Abdsalah S, et al. The impact of organized mammography service screening on breast carcinoma mortality in seven Swedish counties. Cancer 2002;95: 458-69.
Nystr?m L, Andersson I, Bjurstam N, Frisell J, Nordenskj?ld B, Rutqvist LE. Long-term effects of mammography screening: updated overview of the Swedish randomised trials. Lancet 2002;359: 909-19.
Alexander F, Anderson TJ, Brown HK, Forrest APM, Hepburn W, Kirkpatrick AE, et al. years of follow-up from the Edinburgh randomised trial of breast-cancer screening. Lancet 1999;353: 1903-8.
Njor SH, Olsen AH, Bellstr?m T, Dyreborg U, Bak M, Axelsson C, et al. Mammography screening in the county of Fyn November 1993-December 1999. APMIS 2003;111(suppl 110): 1-33.(Anne Helene Olsen, statistician1, Sisse )
Correspondence to: A H Olsen a.h.olsen@pubhealth.ku.dk
Abstract
In the overview of five randomised trials from Sweden, a reduction of 29% was found in breast cancer mortality in women aged 50-69 at randomisation after a follow up of 5-13 years.1 Organised, population based, mammography service screening was introduced on the basis of these results in Copenhagen, the capital of Denmark, in 1991.2 Since then the validity of the trial results and the justification of mammography screening have been debated intensively.3 4 Furthermore, the adaptation of trial results to routine health care is not straightforward. Examining whether the screening programmes actually reduce mortality due to breast cancer is therefore important.
In Denmark, mammography screening was introduced in only three out of 16 administrative regions. The regions without a mammography screening programme thereby provide a natural control group during the full period of follow up. In addition, opportunistic screening has been limited.5 Taking advantage of this "natural experiment," and using the nationwide population and health registers in Denmark, we developed a method to determine the effect of mammography service screening on breast cancer mortality.6 We present here the results of the first 10 years of screening in Copenhagen.
Methods
For the period before screening started, Copenhagen had a significantly higher mortality due to breast cancer than the rest of Denmark (relative risk 1.22, 95% confidence interval 1.10 to 1.35), although there was some variation by age group. This had changed in the screening period, where Copenhagen had a lower breast cancer mortality than the rest of Denmark (0.91, 0.80 to 1.05). When we compared Copenhagen in the screening period with the period before screening, the relative risk was significantly lower than 1 (0.80, 0.68 to 0.94). When we compared the rest of Denmark in the screening period with the period before screening, the relative risk was 1.05 (0.99 to 1.11), again with some variation by age group. When we estimated the effect of the combination of invitation to screening and the interaction term between period and region adjusted for age, period, and region, the relative risk was 0.75 (0.63 to 0.89; table 2).
Table 2 Effect estimates for breast cancer mortality in the Copenhagen mammography screening programme
We estimated the cumulative effect of the combination of invitation to screening and the interaction term between period and region by year of follow up and adjusted for age at entry, period, and region (fig 2). Significance was reached after six years of follow up.
Fig 2 Estimated effect on breast cancer mortality of invitation to mammography screening in Copenhagen, cumulated over years of follow up
For the participants the estimated effect of combining participation in screening and the interaction term between period and region adjusted for age, period, and region resulted in a relative risk of 0.60 (0.49 to 0.74). On the other hand, women invited to screening who did not participate had a relative risk of 1.15 (0.91 to 1.46). On this basis, we estimated that in a situation without screening, participants would be a selected part of the population, with a relative risk of 0.95 compared with the total population. When we adjusted for this selection bias, the relative risk for the participants was 0.63.
When we used the same method as in the breast cancer mortality analysis, the invited population had a total cancer mortality (excluding breast cancer) close to that expected without screening (relative risk 0.96, 0.91 to 1.01).
Discussion
Nystr?m L, Rutqvist LE, Wall S, Lindgren A, Lindqvist M, Ryden S, et al. Breast cancer screening with mammography: overview of Swedish randomised trials. Lancet 1993;341: 973-8.
Mammography screening evaluation group, H:S Copenhagen Hospital Corporation. Mammography screening for breast cancer in Copenhagen April 1991-March 1997. APMIS 1998;106(suppl 83): 1-44.
G?tzsche PC, Olsen O. Is screening for breast cancer with mammography justifiable? Lancet 2000;355: 131-6.
Olsen O, G?tzsche PC. Cochrane review on screening for breast cancer with mammography. Lancet 2001;358: 1340-2.
Olsen AH, Jensen A, Njor SH, Villadsen E, Schwartz W, Vejborg I, et al. Breast cancer incidence after the start of mammography screening in Denmark. Br J Cancer 2003;88: 362-5.
Olsen AH, Njor SH, Vejborg I, Schwartz W, Dalgaard P, Jensen M-B et al. A model for determining the effect of mammography service screening. Acta Oncologica 2005 (in press).
Vejborg I, Olsen AH, Jensen M-B, Rank F, Tange UB, Lynge E. Early outcome of mammography screening in Copenhagen 1991-99. J Med Screen 2002;9: 115-9.
Fischerman K, Mouridsen HT. Danish Breast Cancer Cooperative Group (DBCG). Structure and results of the organisation. Acta Oncologica 1988;27: 593-6.
Andreasen AH, Mouridsen HT, Andersen KW, Lynge E, Madsen M, Olesen KP. Improved prognosis of breast cancer. Ugeskr L?ger 1994;156: 6512-7.
Andreasen AH, Andersen KW, Madsen M, Mouridsen H, Olesen KB, Lynge E. Regional trends in breast cancer incidence and mortality in Denmark prior to mammographic screening. Br J Cancer 1994;70: 133-7.
Blanks RG, Moss SM, McGahan CE, Quinn MJ, Babb PJ. Effect of NHS breast screening programme on mortality from breast cancer in England and Wales, 1990-8: comparison of observed with predicted mortality. BMJ 2000;321: 665-9.
Otto SJ, Fracheboud J, Looman CWN, Broeders MJM, Boer R, Hendriks JHCL, et al. Initiation of population-based mammography screening in Dutch municipalities and effect on breast-cancer mortality: a systematic review. Lancet 2003;361: 1411-17.
Jonsson H, Nystr?m L, T?rnberg S, Lenner P. Service screening with mammography of women aged 50-69 years in Sweden: effects on mortality from breast cancer. J Med Screen 2001;8: 152-60.
Duffy SW, Tabar L, Chen HH, Holmqvist M, Yen MF, Abdsalah S, et al. The impact of organized mammography service screening on breast carcinoma mortality in seven Swedish counties. Cancer 2002;95: 458-69.
Nystr?m L, Andersson I, Bjurstam N, Frisell J, Nordenskj?ld B, Rutqvist LE. Long-term effects of mammography screening: updated overview of the Swedish randomised trials. Lancet 2002;359: 909-19.
Alexander F, Anderson TJ, Brown HK, Forrest APM, Hepburn W, Kirkpatrick AE, et al. years of follow-up from the Edinburgh randomised trial of breast-cancer screening. Lancet 1999;353: 1903-8.
Njor SH, Olsen AH, Bellstr?m T, Dyreborg U, Bak M, Axelsson C, et al. Mammography screening in the county of Fyn November 1993-December 1999. APMIS 2003;111(suppl 110): 1-33.(Anne Helene Olsen, statistician1, Sisse )