BMJ  2005;330:936 (23 April), doi:10.1136/bmj.38398.469479.8F (published 8 March 2005)

Paper

Model of outcomes of screening mammography: information to support informed choices

¹ Screening and Test Evaluation Program, School of Public Health, University of Sydney, NSW 2006, Australia

Abstract

Objective To provide easy to use estimates of the benefits and harms of biennial screening mammography for women aged 40, 50, 60, and 70 years.

Design Markov process model, with data from BreastScreen Australia, the Australian Institute of Health and Welfare, and the Australian Bureau of Statistics.

Main outcome measure Age specific outcomes expressed per 1000 women over 10 years.

Results For every 1000 women screened over 10 years, 167-251 (depending on age) receive an abnormal result; 56-64 of these women undergo at least one biopsy, 9-26 have an invasive cancer detected by screening, and 3-6 have ductal carcinoma in situ (DCIS) detected by screening. More breast cancers (both invasive and DCIS) are diagnosed among screened than unscreened women. For example, among 1000 women aged 50 who have five biennial screens, 33 breast cancers are diagnosed: 28 invasive cancers (18 detected at screening and 10 interval cancers) and five DCIS (all detected at screening). By comparison, among 1000 women aged 50 who decline screening, 20 cancers are diagnosed over 10 years. There are about 0.5, 2, 3, and 2 fewer deaths from breast cancer over 10 years per 1000 women aged 40, 50, 60, and 70, respectively, who choose to be screened compared with women who decline screening at times determined by relevant policy.

Conclusion Benefits and harms of screening mammography are relatively finely balanced. Quantitative estimates such as these can be used to support individual informed choices about screening.

Introduction

Screening mammography is recommended for women aged 50-69 on the evidence that benefits outweigh harms.^{1 2} The issue remains controversial, however, especially for women outside this age group. According to the General Medical Council,³ the UK National Screening Committee,⁴ and others⁵ comprehensive information about screening should be available to support informed choices. General principles on the provision of information about cancer screening include that information should be balanced (describing benefits and harms over a similar time frame, such as 10 years) and that estimates should be presented with a constant denominator (such as per 100 or 1000 people).⁶ Important harms include anxiety, which can be long lasting, generated by false positive results,⁷ and the psychological and physical impact of detection and treatment of disease that would not have been diagnosed without screening (overdetection or detection of inconsequential disease).⁸

Methods

We constructed a Markov process model for two hypothetical cohorts of women under four scenarios. In one cohort women undergo biennial screening over 10 years and in the other cohort they do not (see bmj.com). The model is based on 100% participation in the screening cohort and no participation in the non-screening cohort and thus generates the consequences for women who attend screening regularly versus those who decline it. The first scenario compares women who start screening at age 40 with women who decline screening at age 40 (to estimate the effect of starting screening early). The second and third scenarios model outcomes for women who choose to start screening at age 50 and then continue over the full life of the screening programme—that is, from 50-69 years. As this decision will hold for 20 years, the second scenario provides outcomes for the first 10 years, and the third scenario provides outcomes for the second 10 years of this choice. The last scenario compares outcomes among women aged 70 who have been screened regularly and then choose to continue screening for another 10 years with women who stop screening at 69 years (to estimate the effect of extending screening to 79 years).

We used data from BreastScreen Australia^9-13 to populate the model. These data comprise outcome information for screening and subsequent tests for more than 1.25 million women screened each year. The box summarises assumptions underlying the model. More details and data sources are given on bmj.com.

Each scenario begins with a defined number of women (1000) at a specified starting age. We then apply age specific probabilities to reflect the likely transition of the cohorts through 10 one year cycles.

We also estimated the impact of comorbidity on outcomes as participants in excellent health can expect to gain more from screening, particularly at older ages when competing causes of death increase. For this we used estimates for mortality according to self reported health status (see bmj.com for further details).

Results

Outcomes of screening over 10 years for women aged 40, 50, 60, and 70
The table shows results for all age groups. Using 50 year old women as an example for interpretation, among 1000 women aged 50 who are screened biennially over the next 10 years, 242 will receive an abnormal result and be recalled for assessment. Of these, 178 will have only more imaging and 64 will undergo biopsy. Therefore, over 10 years there is a 24% chance of being recalled and a 6% chance of having at least one breast biopsy. A total of 23 cancers will be detected by screening (18 invasive and five DCIS). A further 10 interval cancers will be diagnosed, giving a total of 33 cancers diagnosed in the screening group. In comparison, among 1000 women aged 50 who decline screening, over 10 years about 20 breast cancers (almost all of which are invasive) are detected. Among the screened women four will die from breast cancer compared with six among the unscreened women; this is in the context of around 31 deaths from all causes in the unscreened group and 29 deaths from all causes in the screened group.

View this table: [in this window] [in a new window]   Outcomes for women who undergo screening compared with those who do not. Figures are cumulative number out of 1000 women over 10 years

 

Similar interpretations apply to the other scenarios. The general pattern is the same for women who choose or decline screening at 40, although the numbers of diagnoses of breast cancer, deaths from breast cancer, and deaths from all causes are lower. For women aged 60 the pattern is again similar but with larger numbers of diagnoses, deaths from breast cancer, and deaths from all causes.

For women who continue screening into their 70s, over 10 years two fewer women per thousand die from breast cancer than in women who stop screening (six v eight deaths from breast cancer). The number of diagnoses of breast cancer in screened women is about 41 and the number in unscreened women about 26. All cause mortality is substantially higher than in younger women, reflecting the increase in deaths from other causes.

Assumptions underlying model Incidence of DCIS in unscreened women (assumed to be 2% of total incidence of breast cancer in unscreened women14) Size of benefit on breast cancer mortality due to screening (relative risk reduction of 37% for women aged 50-7915 16 and 23% for women 40-4916 17) Onset and duration of benefit on breast cancer mortality (benefit accrues linearly to maximal level over first five years after starting screening; benefit declines linearly to nothing over five years after stopping screening) Mortality from causes other than breast cancer (screened and unscreened women experience the same risk of death from causes other than breast cancer)

Sensitivity analyses that varied the relative risk reductions for women over 50 across the range of 20-50% (see bmj.com) resulted in only small changes in the absolute number of deaths related to breast cancer for each age group. With a relative risk reduction of 50%, the number of deaths from breast cancer in screened women decreased from 4.0 to 3.7 for 50 year olds; from 5.1 to 4.5 for 60 year olds; and from 6.2 to 5.1 for 70 year old women.

Effect of self reported health status
Self reported health status had little effect on incidence of or mortality from breast cancer, but, as expected, had a striking effect on the mortality from causes other than breast cancer (see bmj.com).

Discussion

We have presented easy to use, age specific estimates of the benefits and harms of screening mammography. These estimates should give women, clinicians, and service providers full information about mammography screening. In summary, for every 1000 women screened over 10 years, 167-251 (depending on age) receive an abnormal result and are recalled; about 56-64 of these have at least one biopsy. Nine to 26 women (depending on age) have an invasive cancer detected by screening and three to six have DCIS detected by screening. About 0.5, 2, 3, and 2 fewer deaths from breast cancer occur over 10 years among 1000 women aged 40, 50, 60, and 70 years respectively who choose to be screened compared with women who decline screening at these times.

Interpretation and implications for future practice and research
The information presented here is readily usable by women considering screening mammography. In essence the decision to be screened is a gamble; thereis only a small chance of benefit but the stakes are high. Some women will be happy to choose the gamble even though they may experience anxiety, inconvenience, and physical adverse effects; other women will not. Clinicians may be able to use this information to support discussions with women about these possibilities and to support their patients in making a choice that is consistent with their own circumstances and values and preferences. As well as providing information for women aged 50-69 years, it may be useful for clinicians' discussions with patients in "out of target" age groups by making explicit the possible risks and benefits of a decision to be screened. We have incorporated these estimates into decision aids that are currently being tested in Australia. These methods can be applied to different populations and other screening contexts. The effect of such information on decision quality and screening participation is currently unknown but can be tested.

What is already known on this topic Outcomes of screening mammography include benefits (reduced risk of death from breast cancer) and harms (physical and psychological adverse effects from screening and follow-up tests and detection of inconsequential disease) Current information about screening mammography fails to meet women's needs for full and balanced information about these benefits and harms What this study adds This model of screening mammography presents quantitative information about the outcomes of screening in a form suitable to inform decisions about screening It provides information about cumulative benefits and harms over the same time frame (10 years) for women aged 40, 50, 60, and 70 years who are considering screening

---

The formula used to calculate mortality from breast cancer in unscreened women is on bmj.com

This is the abridged version of an article that was posted on bmj.com on 8 March 2005: http://bmj.com/cgi/doi/10.1136/bmj.38398.469479.8F

We thank Erin Mathieu for assistance with proofreading this paper.

Contributors: See bmj.com

Funding: This work was undertaken as part of the screening and test evaluation programme, funded by the National Health and Medical Research Council of Australia (grant No 211205).

Competing interests: None declared.

Ethical approval: Not required.

References

1. BreastScreen Australia and Australian Department of Health and Ageing. Who should have a mammogram? www.breastscreen.info.au/who/index.htm (accessed 2 Feb 2005).
2. US Preventive Services Task Force. Screening for breast cancer. www.ahrq.gov/clinic/uspstf/uspsbrca.htm (accessed 2 Feb 2005).
3. General Medical Council. Seeking patients' consent: the ethical considerations. November 1998. www.gmc-uk.org/global_sections/search_frameset.htm (accessed 2 Feb 2005).
4. UK National Screening Committee. Second report of the UK national screening committee. www.nsc.nhs.uk/pdfs/secondreport.pdf (accessed 2 Feb 2005).
5. Thornton H, Edwards A, Baum M. Women need better information about routine mammography. BMJ 2003;327: 101-3.[Free Full Text]
6. Barratt AL, Trevena L, Davey HM, McCaffery K. Use of decision aids to support informed choices about screening. BMJ 2004;329: 507-10.[Free Full Text]
7. Drossaert CHC, Boer H, Seydel ER. Does mammographic screening and a negative result affect attitudes towards future breast screening? J Med Screen 2001;8: 204-12.[Abstract/Free Full Text]
8. Schwartz LM, Woloshin S, Fowler FJ, Welch HG. Enthusiasm for cancer screening in the United States. JAMA 2004;291: 71-78.[Abstract/Free Full Text]
9. Australian Institute of Health and Welfare. BreastScreen Australia monitoring reports 1998-99, 1999-2000 and 2000-2001. Cancer series numbers 25 and 26. Canberra: Australian Institute of Health and Welfare, 2003 (CAN 20 and CAN 21).
10. Australian Institute of Health and Welfare. BreastScreen Australia achievement report 1997-1998. Cancer series number 13. Canberra: Australian Institute of Health and Welfare, 2000 (CAN 8).
11. Queensland Health. BreastScreen Queensland annual statistical report for 1999. Brisbane: Queensland Health, 2001.
12. BreastScreen Victoria. BreastScreen Victoria 2000 and 2001 annual statistical reports. Melbourne: BreastScreen Victoria, 2002-3.
13. BreastScreen SA. BreastScreen SA statistical report 1999-2000. Adelaide: BreastScreen SA, 2003.
14. Van Zee KJ, Liberman L, Samli B, Tran KN, McCormick B, Petrek JA, et al. Long term follow-up of women with ductal carcinoma in situ treated with breast-conserving surgery: the effect of age. Cancer 1999;86: 1757-67.[CrossRef][ISI][Medline]
15. Kerlikowske K, Grady D, Rubin SH, Sandrock C, Ernster VL. Efficacy of screening mammography: a meta-analysis. JAMA 1995;273: 149-54.[Abstract]
16. Glasziou P. Meta-analysis adjusting for compliance: the example of screening for breast cancer. J Clin Epidemiol 1992;45: 1251-6.[CrossRef][ISI][Medline]
17. Irwig L, Glasziou P, Barratt A, Salkeld G. Review of the evidence about the value of mammographic screening in 40-49 year old women. Kings Cross, New South Wales: NHMRC National Breast Cancer Centre, 1997.

(Accepted 9 February 2005)

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

Relevant Articles

Informed choice for screening: implications for evaluation

Les Irwig, Kirsten McCaffery, Glenn Salkeld, and Patrick Bossuyt
BMJ 2006 332: 1148-1150. [Full Text] [PDF]

Ramifications of screening for breast cancer: More debate and better information still needed

Hazel Thornton
BMJ 2006 332: 728. [Extract] [Full Text]

Content of invitations for publicly funded screening mammography

Karsten Juhl Jørgensen and Peter C Gøtzsche
BMJ 2006 332: 538-541. [Full Text] [PDF]

Model of outcomes of screening mammography: Spontaneous regression of breast cancer may not be uncommon

Per-Henrik Zahl and Jan Mæhlen
BMJ 2005 331: 350. [Extract] [Full Text]

Model of outcomes of screening mammography: Information needs to support informed choices

Peter C Gøtzsche and Karsten J Jørgensen
BMJ 2005 331: 350-351. [Extract] [Full Text]

Model of outcomes of screening mammography: Women's decisions about screening depend on many factors

Sue M Lockwood, Nicola Bruce, and Rosetta Manaszewicz
BMJ 2005 331: 351. [Extract] [Full Text]

Improve your patients' informed consent about screening mammography
BMJ 2005 330: 0. [Full Text]

Preventive medicine makes us miserable

Fiona Godlee
BMJ 2005 330: 0. [Extract] [Full Text] [PDF]

Making decisions about mammography

Paul Taylor
BMJ 2005 330: 915-916. [Extract] [Full Text] [PDF]

Use of decision aids to support informed choices about screening

Alexandra Barratt, Lyndal Trevena, Heather M Davey, and Kirsten McCaffery
BMJ 2004 329: 507-510. [Extract] [Full Text] [PDF]

Incidence of breast cancer in Norway and Sweden during introduction of nationwide screening: prospective cohort study

Per-Henrik Zahl, Bjørn Heine Strand, and Jan Mæhlen
BMJ 2004 328: 921-924. [Abstract] [Full Text] [PDF]

Women need better information about routine mammography

Hazel Thornton, Adrian Edwards, and Michael Baum
BMJ 2003 327: 101-103. [Extract] [Full Text] [PDF]

This article has been cited by other articles:

• HAGEN, S., GOODWIN, E., SINCLAIR, L. (2008). Sitting vs Standing During Screening Mammography. radtech 79: 214-220 [Abstract] [Full text]  
• Mathieu, E., Barratt, A., Davey, H. M., McGeechan, K., Howard, K., Houssami, N. (2007). Informed Choice in Mammography Screening: A Randomized Trial of a Decision Aid for 70-Year-Old Women. Arch Intern Med 167: 2039-2046 [Abstract] [Full text]  
• Irwig, L., McCaffery, K., Salkeld, G., Bossuyt, P. (2006). Informed choice for screening: implications for evaluation.. BMJ 332: 1148-1150 [Full text]  
• Castells, X., Molins, E., Macia, F. (2006). Cumulative false positive recall rate and association with participant related factors in a population based breast cancer screening programme.. J. Epidemiol. Community Health 60: 316-321 [Abstract] [Full text]  
• Thornton, H. (2006). Ramifications of screening for breast cancer: more debate and better information still needed.. BMJ 332: 728-728 [Full text]  
• Jorgensen, K. J., Gotzsche, P. C (2006). Content of invitations for publicly funded screening mammography.. BMJ 332: 538-541 [Full text]  
• Baker, S. G., Gotzsche, P. C., Baglioni, P., Smith, D. W., Retsky, M. W., Demicheli, R., Hrushesky, W. J.M., Berry, D. A., Plevritis, S. K., Fryback, D. G. (2006). Screening and breast cancer.. NEJM 354: 767-769 [Full text]  
• Lockwood, S. M, Bruce, N., Manaszewicz, R. (2005). Model of outcomes of screening mammography: Women's decisions about screening depend on many factors. BMJ 331: 351-351 [Full text]  
• Zahl, P.-H., Maehlen, J. (2005). Model of outcomes of screening mammography: Spontaneous regression of breast cancer may not be uncommon. BMJ 331: 350-350 [Full text]  
• Gotzsche, P. C, Jorgensen, K. J (2005). Model of outcomes of screening mammography: Information needs to support informed choices. BMJ 331: 350-351 [Full text]  
• Taylor, P. (2005). Making decisions about mammography. BMJ 330: 915-916 [Full text]  

Rapid Responses:

Read all Rapid Responses

Over-detection or spontaneous regression of breast cancer?

Per-Henrik Zahl, et al.
bmj.com, 11 Mar 2005 [Full text]

Outcomes of screening mammography: information to support informed choices

Peter C Gøtzsche, et al.
bmj.com, 15 Mar 2005 [Full text]

What is important to women making decisions about screening?

Sue M Lockwood, et al.
bmj.com, 26 Apr 2005 [Full text]

Is the desired effect of mammography screening dwindling away before our eyes?

Friederike M. Perl
bmj.com, 6 May 2005 [Full text]

Does screening mammography cause cancers?

Jayant S Vaidya
bmj.com, 16 May 2005 [Full text]