Breast screening - potential effects

This page is based on the CancerStats report Breast Screening - UK published in 2003.

The page presents information on the potential effect of breast screening including, registrations of carcinoma in situ, incidence of invasive cancer, mortality, survival and anxiety.

The potential effects of screening

 
 

Registrations of carcinoma in situ

Ductal carcinoma in situ (DCIS) registrations have increased markedly since the introduction of breast screening, because it is a condition that is usually not palpable and therefore is mostly diagnosed by mammography. DCIS accounts for approximately 20% of screen-detected cancers.

Between 1995 and 1999 there were, on average, 2,732 registrations of carcinoma in situ in the UK per year which equates to a rate of 9.3 per 100,000 women.The peak age groups for numbers and rates of DCIS are the same as the screening age groups ( Figure 5.1).

Figure 5.1: Carcinoma insitu female breast cancer: Average number of new cases and rates by age, Uk, 1995-1999 ICD 10 D05

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Critics of the breast screening programme have voiced concerns that identifying DCIS is overdiagnosis of breast cancer, as these lesions may never progress or threaten the woman’s life. 1 However, the majority of screen-detected DCIS is high grade (69%) and necrotic (87%), and there is growing and convincing evidence that the detection of high grade and necrotic DCIS by screening and its subsequent treatment prevents the development of high grade invasive cancer with poor prognosis. 2-4

Treatment of DCIS is usually wide area excision with or without radiotherapy. Recent results from a multi-national randomised controlled trial have shown the effectiveness of radiotherapy after complete local excision, but little evidence for the use of tamoxifen. 5 If the area of abnormality is extensive, a mastectomy may be more appropriate. Currently around 30% of screen-detected DCIS is treated with mastectomy. 6

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Incidence of invasive cancer

The incidence of breast cancer in Britain has increased from an age standardised rate of 75 per 100,000 women in 1979 to 114 per 100,000 women in 2001. 7-10 Further details are in the Breast Cancer section. Introduction of the Breast Screening Programme in the UK in 1988 led to a transient additional increase in incidence, lasting four to seven years, for women aged 50-64 years, but the underlying increase in incidence predates screening, continues today, and is evident in all ages between 45 and 99 years 11 ( Figure 5.2). 7-10

Figure 5.2: Age-specific incidence rates of invasive female breast cancer, GB, 1979-2001

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Mortality

Several analyses combining the results of published studies have been carried out to estimate the effect of mammography on mortality from breast cancer.

The most recent - a meta-analysis of seven randomised trials - concluded that there was a 15-20% reduction in risk of death from breast cancer in women attending mammography. The authors calculated that for 2,000 women attending screening over a period of 10 years, one life would be saved. At the same time, 10 women would be falsely diagnosed with cancer as a result of screening and undergo unnecessary treatment as a result. 30

A meta-analysis of nine randomised controlled trials and four observational studies showed that mortality from breast cancer is reduced by 26% in women aged 50-74 who are offered screening mammography (relative risk = 0.74, 95% confidence interval (CI) 0.66 to 0.83). 12 The same meta-analysis did not show a mortality reduction for women aged under 50 (relative risk = 0.93, 95% CI 0.76 to 1.13).

Another systematic review, published in 2000, concluded that screening for breast cancer with mammography is unjustified. 13 However, this review has been widely criticised for being far too stringent. 14-16

The reviewers excluded six out of eight randomised controlled trials on the basis of potential age imbalances between intervention and control groups, but the age differences were very small. The largest age difference was five months, and this was likely to be due to the cluster design of the trial (the Swedish Two County Trial). The authors of this trial have now adjusted for the differences in age and observed a significant reduction in breast cancer mortality associated with breast screening of 30%. 17

A recent analysis of mortality from breast cancer reported a 21% absolute reduction in observed death rates from breast cancer by 1998, compared with expected mortality rates in the absence of screening. The authors estimated that overall breast screening resulted in a 6.4% reduction in mortality, the rest of the decrease being due to improved treatment and earlier diagnosis independent of screening. 18

The controversy surrounding the effectiveness of breast screening continued with the publication in 2001 of an adapted version of the 2000 review. 19

This review claimed to strengthen and confirm the original findings questioning the impact of breast screening on mortality. 13

In a more recent review the International Agency for Research on Cancer (IARC) concluded that many of the criticisms of screening were unsubstantiated, and that breast screening of women aged 50-69 results in a 25% reduction in breast cancer mortality in women invited for screening (relative risk = 0.75, 95% CI 0.67 to 0.85).

The review also showed that screening women aged 40-49 does not significantly reduce mortality (relative risk = 0.81, 95% CI 0.65 to 1.01) 20 Amongst women who actually attend mammography, the mortality reduction has been estimated to be 35% for those aged 50-69 years at entry to screening. 20

The debate has continued: the methodology and conclusions of the 2000 and 2001 reviews have been recently challenged 21, 22 whilst the original authors continue to defend their position. 23

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Survival

Breast cancer survival rates are worse the later the stage of the disease at diagnosis ( Figure 5.3). 24

Figure 5.3 : 0-10 year relative survival for cases of breast cancer, by stage diagnosed, West Midlands, 1985-1989 followed up to the end of 1999, as at January 2002

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Over 20% of screen-detected cancers are non-invasive (DCIS), and a further 40% are tumours under 15mm. Invasive cancers detected while small are less likely than larger tumours to have spread to local lymph nodes or distant sites and therefore tend to be earlier stage cancers with a good prognosis. More details are given in the Breast Cancer section.

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Anxiety

False positive results for breast screening can cause anxiety, as well as prompt further invasive investigations. A large UK study has shown that anxiety levels in women who are recalled and then found to be disease free are significantly higher during the year after their recall appointment than in women who receive negative results at initial screening. 25-27 For some women, anxiety persisted at three years after the recall appointment, and this could affect the attendance rates for subsequent screens. 28 The results about anxiety in false positive women have been confirmed in Sweden. 29

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References for effect of breast screening

  1.  Baum, M., Review of ABC of breast disease., in Journal of Medical Screening. 1995. p. 233.
  2.  Evans, A.J., et al., Screen detected ductal carcinoma in situ (DCIS): overdiagnosis or an obligate precursor of invasive disease? J Med Screen, 2001. 8(3): p. 149-51
  3.  Feig, S.A., Ductal carcinoma in situ. Implications for screening mammography. Radiol Clin North Am, 2000. 38(4): p. 653-68, vii
  4.  Maxwell, A.J., et al., A study of breast cancers detected in the incident round of the UK NHS Breast Screening Programme: the importance of early detection and treatment of ductal carcinoma in situ. Breast, 2001. 10(5): p. 392-8
  5.  Houghton, J., et al., Radio therapy and tamoxifen in women with completely excised ductal carcinoma in situ of the breast in the UK, Australia, and New Zealand: randomised controlled trial. Lancet, 2003. 362(9378): p. 95-102
  6.  NHSBSP, B., An audit of screen detected breast cancers for the year of screening April 2001 - March 2002. Presented at BASO, 2nd April 2003. 2003.
  7.  Office for National Statistics, Cancer Statistics registrations: Registrations of cancer diagnosed in 2000, England. Series MB1 no.31. 2003, National Statistics: London.
  8.  ISD Online, Cancer Incidence and Mortality in Scotland. 2004, Information and Statistics Division, NHS Scotland.
  9.  Welsh Cancer Intelligence and Surveillance Unit, Cancer Incidence in Wales 1992-20012002
  10.  Northern Ireland Cancer Registry, Cancer Incidence and Mortality in Northern Ireland. 2002.
  11.  Coleman, M., Trends in breast cancer incidence, survival, and mortality. Lancet, 2000. 356(9229): p. 590
  12.  Kerlikowske, K., et al., Efficacy of screening mammography. A meta-analysis. Jama, 1995. 273(2): p. 149-54
  13.  Gotzsche, P.C. and O. Olsen, Is screening for breast cancer with mammography justifiable? Lancet, 2000. 355(9198): p. 129-34
  14.  de Koning, H.J., Assessment of nationwide cancer-screening programmes. Lancet, 2000. 355(9198): p. 80-1
  15.  Duffy, S.W., Interpretation of the breast screening trials: a commentary on the recent paper by Gotzsche and Olsen. Breast, 2001. 10(3): p. 209-12
  16.  Woolf, S., Taking critical appraisals to extremes: the need for balance in the evaluation of evidence (editorial). Family Practice, 2000. 49(12): p. 1081-1085
  17.  Duffy, S.W., et al., The Swedish Two-County Trial of mammographic screening: cluster randomisation and end point evaluation. Ann Oncol, 2003. 14(8): p. 1196-8
  18.  Blanks, R.G., et al., 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(7262): p. 665-9
  19.  Olsen, O. and P.C. Gotzsche, Cochrane review on screening for breast cancer with mammography. Lancet, 2001. 358(9290): p. 1340-2
  20.  IARC, Effectiveness of Screening: Breast Cancer Screening. IARC Handbooks of Cancer Prevention, ed. B.F. Vainio H. Vol. 7. 2002, Lyon: IARC Press. p.119-156.
  21.  Freedman, D.A., D.B. Petitti, and J.M. Robins, On the efficacy of screening for breast cancer. Int J Epidemiol, 2004. 33(1): p. 43-55
  22.  Freedman, D.A.P., D.B. Robins, J.M., Rejoinder. International Journal of Epidemiology, 2004. 33
  23.  Gotzsche, P.C., On the benefits and harms of screening for breast cancer. Int J Epidemiol, 2004. 33(1): p. 56-64; discussion 69-73
  24.  West Midlands Cancer Intelligence Unit, 0-10 year relative survival for cases of breast cancer by stage diagnosed in the West Midlands 1985-1989 followed up to the end of 1999, as at January 2002. 2002.
  25.  Brett, J., A multi-centre follow-up study to assess the anxiety and opinions of women one month before their next routine breast screening appointment, having previously attended three years earlier. University of Oxford. 1999.
  26.  Brett, J., J. Austoker, and G. Ong, Do women who undergo further investigation for breast screening suffer adverse psychological consequences? A multi-centre follow-up study comparing different breast screening result groups five months after their last breast screening appointment. J Public Health Med, 1998. 20(4): p. 396-403
  27.  Ong, G., J. Austoker, and J. Brett, Breast screening: adverse psychological consequences one month after placing women on early recall because of a diagnostic uncertainty. A multicentre study. J Med Screen, 1997. 4(3): p. 158-68
  28.  Brett, J. and J. Austoker, Women who are recalled for further investigation for breast screening: psychological consequences 3 years after recall and factors affecting re-attendance. J Public Health Med, 2001. 23(4): p. 292-300
  29.  Olsson, P., et al., Women with false positive screening mammograms: how do they cope? J Med Screen, 1999. 6(2): p. 89-93
  30.  Gotzsche PC, Nielsen M. Screening for breast cancer with mammography.Cochrane Database Syst Rev 2006(4):CD001877.