BMJ  2006;332:499-500 (4 March), doi:10.1136/bmj.332.7540.499

Editorial

Screening for breast cancer

Time to accept that, despite limitations, it does save lives

Few topics in medicine have been the subject of so much debate and controversy as breast screening by mammography. The value of screening in reducing mortality has been questioned not only by sceptics¹ but also by those involved in setting up and running screening programmes.^{2 3} The latest addition to the debate is a report published last week by the Advisory Committee on Breast Screening, summarising results from the English breast screening programme.⁴ Although the authors are respected members of the "breast scientific community," they cannot be considered to be independent because they are involved in the delivery and organisation of the programme. What does the report tell us about the current status of breast screening?

Many of the early breast screening trials have been criticised because groups, rather than individuals, were randomised. In 2000 Gøtzsche and Olsen excluded trials that randomised groups of women from their analysis and found no reduction in mortality.¹ ears later a review of all trials by the International Agency for Research into Cancer concluded that mammographic screening in women aged 50-69 did reduce mortality from breast cancer.⁵ The agency disagreed with the scientific justification given by Gøtzsche and Olsen for excluding the results of several of the Swedish randomised trials from their review.

With the mammographic equipment available when the trials were performed it is surprising that sufficient numbers of small cancers were detected to reduce subsequent mortality. During the 17 years of the UK breast screening programme there have been important improvements: better mammography machines, higher resolution film, an increase in the number of views at each screening round, and double reading. The report estimates that breast screening now saves 1400 lives per year at a cost of only £3000 per year of life saved. For every 400 women screened over a 10 year period, one less woman dies from breast cancer than would have died had they not been screened. This equates to one in eight fewer breast cancer deaths in the target age group. These excellent results are consistent with studies showing that screening is responsible for 28-65% (median 46%) of the fall in deaths from breast cancer seen over the past few years.⁶ Breast screening does save lives—and it is cost effective.

One criticism of screening by Gøtzsche and Olsen was that because screening detects some cancers that would never have been diagnosed during the patient's lifetime, the overall number of women who undergo mastectomy each year increases.¹ If screening is to save lives then it must bring forward the time when a breast cancer is diagnosed, so inevitably some women will die from other causes before the cancer becomes clinically evident. The Advisory Committee on Breast Screening acknowledges that about one in eight women with cancers diagnosed by screening would never have had their cancer diagnosed if they had not gone for screening.⁴ The mastectomy rate in women with cancers detected on screening is lower than the rate in women who present with symptoms, so the report estimates that one in eight women with breast cancer who are routinely screened is spared mastectomy. It is difficult from the data provided in the report to confirm these figures, but other studies have reported similar findings,⁷ so this counters another concern aired by the sceptics of breast screening.

Another issue of concern is the rate of recall of women for assessment who do not have cancer. The report notes that approximately 1 in 8 of all women who are screened three times over a 10 year period will be recalled at least once. This seems high and the frequency of these "false positives" varies considerably between screening centres. For instance, recall rates at the first screening round vary from 4% to 19% in different centres. Although this range reflects variations in the ethos of screening units, quality assurance guidelines and regular external review are essential to minimise such variation. Although recall rates are far lower in the United Kingdom than in programmes in the United States,⁸ recall causes considerable anxiety, which can persist and add costs.⁴ Digital mammography, which increases specificity, may reduce the recall rate.⁹

The report gives no reliable data on interval cancers (cancers diagnosed in the (three year) period between mammographic screening rounds), and the Advisory Committee on Breast Screening acknowledges that the screening programme needs to refine its method of collecting interval cancer rates. The expected rate in the first year is 0.45 per 1000 women screened—but the million women study reported a higher rate: 0.82 per 1000 women.¹⁰ Interval cancer rates reflect the quality of screening, and without regional data it is difficult to be certain that all units are delivering high quality screening.

Another criticism of the UK screening programme has been the emphasis on persuading women to attend rather than allowing them to choose on the basis of the potential benefits and risks.¹¹ The report outlines the effort, over recent years, to provide women with sufficient information to make an informed choice. The current national leaflet presents not only the benefits but also the limitations of screening, and further information is available from CancerBacup (www.cancerbacup.org.uk).

The UK breast screening programme has carried out research into refining and evaluating the screening process and also into prevention and treatment trials. The improvement in imaging has also benefited patients with symptoms. The evidence in the report indicates that it is finally time to accept that although breast screening by mammography is far from perfect it is worth while. Criticisms about the early trials are no longer relevant. Breast screening has moved on and is looking to the future, and so should the sceptics.

Edinburgh Breast Unit, Western General Hospital, Edinburgh EH4 2XU
(mike.dixon{at}ed.ac.uk)

---

Competing interests: None declared.

See also Analysis and comment p 538

References

1. Gøtzsche PC, Olsen O. Is screening for breast cancer with mammography justifiable? Lancet 2000;355: 129-34.[CrossRef][ISI][Medline]
2. Roberts MM. Breast screening: time for a rethink? BMJ 1989;299: 1153-5.[ISI][Medline]
3. Baines CJ. Rethinking breast screening—again. BMJ 2005;331: 1031.[Free Full Text]
4. Advisory Committee on Breast Cancer Screening. Screening for breast cancer in England: past and future. Sheffield: NHS Cancer Screening Programmes, 2006. (NHSBSP publication No 61.) www.cancerscreening.nhs.uk/breastscreen/publications/nhsbsp61.pdf (accessed 27 Feb 2006).
5. International Agency for Research on Cancer. Breast cancer screening. Lyon: IARC Press, 2002. (IARC Handbooks of Cancer Prevention, vol 7.)
6. Berry DA, Cronin KA, Plevritis SK, Fryback DG, Clarke L, Zelen M, et al. Effect of screening and adjuvant therapy on mortality from breast cancer. N Engl J Med 2005;353: 1784-92.[Abstract/Free Full Text]
7. Paci E, Duffy SW, Giorgi D, Zappa M, Crocetti E, Vezzosi V, et al. Are breast cancer screening programmes increasing rates of mastectomy? Observational study. BMJ 2002;325: 418.[Free Full Text]
8. Smith-Bindman R, Chu PW, Miglioretti DL, Sickles EA, Blanks R, Ballard-Barbash R, et al. Comparison of screening mammography in the United States and the United Kingdom. JAMA 2003;29: 2129-37.
9. Pisano ED, Gatsonis C, Hendrick E, Yaffe M, Baum JK, Acharyya S, et al. Diagnostic performance of digital versus film mammography for breast-cancer screening. N Engl J Med 2005;353: 1773-83.[Abstract/Free Full Text]
10. Million Women Study Collaborators. Breast cancer and hormone replacement therapy in the million women study. Lancet 2003;362: 419-27.[CrossRef][ISI][Medline]
11. Thornton H, Edwards A, Baum M. Women need better information about routine mammography. BMJ 2003;327: 101-3.[Free Full Text]

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