Breast screening statistics

Breast cancer (invasive) is the most common cancer in the UK (2010), with 49,564 cases in 2010 accounting for 31% of all female cases. There were a further 5,765 cases of in situ breast carcinoma (all in situ ICD-10 D05) in women in the UK in 2010, of which 83% were DCIS (ICD-10 D05.1). In 1986, the Forrest Report recommended the introduction of a national breast screening programme on the basis of trials undertaken in the United States and Sweden.[1]

Across the UK women aged 50 to 70 are invited for breast screening with mammography every three years by the NHS Breast Screening Programme(NHSBSP). Women over 70 are eligible for breast screening but are not automatically invited. In England a trial is taking place to look at the possible benefits of extending breast screening so that women aged 47 to 50 and 70 to 73 are also invited.[2]

The principle benefit of breast screening is earlier detection, which facilitates less aggressive treatment, improving prognosis and ultimately, it is hoped, saving lives. However, there are some well-documented harms related to screening including radiation exposure, pain and the physiological consequences of false positive, false negative and true positive results. Many observers consider overdiagnosis, the detection of cancers which would have never caused harm in the woman’s lifetime, to be by far the greatest harm.

Screening works by detecting cancer early and this means that a screened population is, at least initially, likely to have a higher incidence of breast cancer. An increase in breast cancer cases can be clearly seen in the incidence trends increasing in the early 1990s for the 50 to 64 age group and later for the 65 to 69 age group. As the breast cancer has been detected earlier via screening we then expect to see a lower incidence in later age groups. Some screen-detected cancers, however, may never progress to become symptomatic. These are known as overdiagnosed cases.

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Breast cancer (invasive) is the most common cancer in the UK (2010), with 49,564 cases in 2010 accounting for 31% of all female cases. There were a further 5,765 cases of in situ breast carcinoma (all in situ ICD-10 D05) in women in the UK in 2010, of which 83% were DCIS (ICD-10 D05.1). In 1986, the Forrest Report recommended the introduction of a National Health Service Breast Screening Programme (NHSBSP) offering three yearly mammography Open a glossary item screening to women aged 50 to 64.[1] The breast screening programme was set up in England in 1988, and 110,000 women between the ages of 50 and 64 accepted their invitation for screening in financial year (FY) 1988/1989.[2]

Originally, all UK women aged 50 to 64 registered with a GP were invited for screening every three years but since 2004 this has been extended to include women aged 65 to 70 years. Women over 70 are eligible for breast screening but are not automatically invited. In England a trial is taking place to look at the possible benefits of extending breast screening so that women aged 47 to 50 and 70 to 73 are also invited.[3]

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In Financial year (FY) 2009/10, 2,754,885 women aged 45 to 74 were invited to breast screening in the UK and 2,018,403 (73%) attended as a result.[1] There were around 16,500 detections by the screening, of which around 13,200 (80%) were invasive breast cancers and around 3,300 were ductal carcinoma in situ (DCIS).

In the target screening group of women aged 50 to 70 there were around 15,500 detections, around 12,500 (80%) of which were invasive breast cancers and around 3,100 were DCIS. Around 4% of women screened were recalled for assessment and around 1,500 women aged 50 to 70 had a biopsy which showed the tumour was benign.

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In England during financial year (FY)2010/11, the number of people invited to screening was more than 2.4 million and uptake (the measure of women who were invited for screening who attend) was 1.8 million (73%). Nearly 95% of women screened were within the 50 to 70 age group.[1] The percentage of women aged 50 to 54 attending screening was slightly lower (72%) than in the women aged 55 to 70 but remained higher than women aged 45 to 49 (71%) and those over 70 (63%).

Number of Women Invited to and Attending Breast Screening, England, FY2010/11

Age Number Invited to Screening Number attending screening Uptake (%)
45-49 114,161 80,722 70.7
50-54 635,874 458,279 72.1
  50-52 386,723 280,117 72.4
53-54 249,151 178,162 71.5
55-59 560,427 411,707 73.5
60-64 593,098 444,014 74.9
65-70 513,487 375,860 73.2
Over 70 19,450 12,194 62.7
England 2,436,497 1,782,776 73.2

References

  1. Information Centre for Health and Social Care. Summary statistics on breast cancer and the NHS Breast Screening Programme, 2001 to 2011. (Accessed October 2012).
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The percentage uptake has fallen slightly in England since 2001 decreasing from 75% to 73% in women aged 50 to 64 from FY2000/01 to FY2010/11, and from 74% to 73% in women aged 50 to 70 from FY2002/03 to FY2010/11.[1]

Percentage Uptake (Women Invited to Screening who Attended), England, FY2000/01-2010/11

Despite the decrease in uptake, coverage (the total number of women who have attended screening by invitation or by GP or self referral) for women 50 to 64, is currently increasing, rising from a low of 69% in FY2003/04 to 71% in FY2010/11.

Percentage of Women Aged 50 to 64 Screened, England, FY2000/1-2010/11

The number of women aged 50 to 64 referred for assessment as a result of screening has fallen from around 60,200 (4% of women screened) in FY2000/01 to around 53,200 (3%) in FY2010/11.

Percentage of Invited Women who were Referred, England, FY2000/01-2010/11

For women aged 50 to 64 the detection rate of cancers and tumours by the National Health Service Breast Screening Programme (NHSBSP) increased sharply between FY2000/01 and FY2003/04, from 6.1 per 1,000 women screened to 7.2, but has since stabilised at around 7 per 1,000. The detection rate for women aged 50 to 70 has continued to be slightly higher than for women aged 50 to 64 and is currently 7.6 per 1,000 women screened.

Detection Rate for Women Screened, England, FY2000/01-2010/11

References

  1. Information Centre for Health and Social Care. Summary statistics on breast cancer and the NHS Breast Screening Programme, 2001 to 2011. (Accessed October 2012).
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The percentage of uptake of breast screening in England is above the National Health Service Breast Screening Programme (NHSBSP) minimum standard of 70% in all strategic health authorities except London, where it is around 64%. This low uptake in London is thought to be related to both socio-economic deprivation and ethnicity.[1] Outside of London uptake varies from 72% in the North West to around 79% in the East Midlands for women aged 50 to 70 to. There is not much variation by age.

Screening Activity, By Strategic Health Authority, Women, FY2010/11

Strategic Health Authority Uptake (%) Rate of Cancers Detected per 1,000 women screened Coverage (%)
50 to 64 50 to 70 50 to 70 53 to 70
East Midlands 78.8 78.6 7.3 81.8
South West 76.6 76.4 7.6 79.5
East of England 76.6 76.5 7.6 79.0
North East 75.7 75.7 7.4 79.0
South Central 75.2 75.2 8.0 79.3
West Midlands 74.4 74.3 7.5 77.2
Yorkshire & the Humber 74.2 74.1 7.7 78.3
South East Coast 73.5 73.6 7.9 77.6
North West 72.2 72.0 7.9 75.0
London 63.9 63.6 7.2

68.9

References

  1. Renshaw C, Jack RH, Dixon S, Møller H, Davies EA. Estimating attendance for breast cancer screening in ethnic groups in London. BMC Public Health 2010;10:157.
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A number of randomised trials of women aged 50 and over have also suggested that mortality from breast cancer is reduced in those offered screening compared with unscreened controls (for those trials where there is a reduction, it is not always statistically significant).

Relative Risk of Breast Cancer Death in Screening With Mammography Versus No Screening in Randomised Control Trials with 13 years follow up

Randomised Control Trial (Year) Relative Risk for Women All Ages (Confidence Interval) Relative Risk for Women Aged 50 and Over (Confidence Interval)
New York (1963) 0.83 (0.70-1.00) 0.78 (0.60-1.01)
Malmo (1976) 0.81 (0.61-1.07) 0.86 (0.64-1.16)
Kopparberg (1977) 0.58 (0.45-0.76) 0.55 (0.42-0.73)
Ostergotland (1978) 0.76 (0.61-0.95) 0.71 (0.56-0.91)
Canada I (1980) 0.94 (0.74-1.27) N/A
Canada II (1980) 1.02 (0.78-1.33) 1.02 (0.78-1.33)
Stockholm (1981) 0.73 (0.50-1.06) 0.64 (0.41-1.01)
Gothenburg (1982) 0.75 (0.58-0.97) 0.83 (0.60-1.15)
UK Age (1991) 0.83 (0.66-1.04) N/A

Adapted from the Cochrane Review Analysis 1.2 and 1.6.[1]

Controversy, however, continues over the effectiveness of breast screening programmes.[1,2]

For example, the randomised control trials have been criticised for the poor quality of randomisation, for differential exclusions between study and control groups, and some have suggested that the findings from the trials are no longer relevant to the current screening programme because drug treatment has improved so markedly.

Reduction in the relative risk

A number of interested parties have carried out meta-analyses Open a glossary item of the randomised control trials to try to improve the estimate for the reduction in breast cancer mortality due to screening. Although there were differences in which trials were included, how the trials were run, and the follow up period used in the analyses, the results from the meta-analyses are reasonably consistent.[3]

Relative Risk of Breast Cancer Death in Screening With Mammography Versus No Screening in a Number of Meta-Analyses

Meta Analysis Analysis Details Relative Risk (95% Confidence Interval)
Independent Breast Screening review 13-year follow-up in trials reported in the Cochrane Review, Random-effects meta-analysis 0.80 (0.73-0.89)
Cochrane Review 13-year follow-up in ‘adequately’ and ‘sub-optimally’ randomised trials, Fixed-effect meta-analysis 0.81 (0.74–0.87)
Cochrane Review 13-year follow-up in ‘adequately’ and ‘sub-optimally’ randomised trials, in women 50 and over, Fixed-effect meta-analysis 0.77 (0.69–0.86)
Cochrane Review 13-year follow-up in ‘adequately’ randomised trials, Fixed-effect meta-analysis 0.90 (0.79–1.02)
US Task Force Trials selected from a systematic search, women aged 50–59 years, Random-effects meta-analysis 0.86 (0.75–0.99)
US Task Force Trials selected from a systematic search, women aged 60–69 years, Random-effects meta-analysis 0.68 (0.54–0.87)
Canadian Task Force Trials selected from a systematic search, Random-effects meta-analysis 0.79 (0.68–0.90)
Duffy et al Review of all trials and age groups 0.79 (0.73–0.86)

Adapted from the Independent Panel on Breast Screening.[3]

Absolute risk

There has been much greater disagreement about the absolute risk reduction due to screening in comparison to the relative risk, as shown by the varying estimates of the numbers of women who would need to be screened to prevent one death.[4]

This stems in part from the variation in several factors, including the age at which regular screening starts, the period over which it continues, and the duration of follow-up after screening.[5]

Estimated Numbers of Women Needed To Screen to Prevent One Breast Cancer Death

Study Analysis Details Number Needed to Screen / Invited
Independent Breast Screening review Based on an RR reduction of 20% for women aged 55–79 years in the UK. 235 women invited
Cochrane Review Absolute risk reduction based on the 13-year follow-up in the trials considered ‘adequately randomised’. 2000 women invited
US Task Force Based on 7 years of screening and 13 years of follow-up. 1339 women invited aged 50–59 years 377 invited aged 60–69 years
Canadian Task Force Women aged 50–69 years screened every 2–3 years for about 11 years. 720 women screened
Duffy et al Based on 22-year follow-up of women aged 50–69 years in the Swedish Two-County trial, assuming that the absolute risk reduction for the 7 years of screening can be multiplied up to reflect 20 years in the UK screening programmes. 113 women screened
Beral et al Women aged 50–70 years regularly screened for 10 years, based on summary of published evidence. 400 women screened

Adapted from the Independent Panel on Breast Screening.[3]

References

  1. Gøtzsche PC, Nielsen M Screening for breast cancer with mammography Cochrane Database System Reviewed 2011
  2. Autier P, Boniol M, Gavin A, Vatten LJ Breast cancer mortality in neighbouring European countries with different levels of screening but similar access to treatment: trend analysis of WHO mortality database British Medical Journal. 2011; 343(7818)
  3. Independent UK Panel on Breast Cancer Screening. The benefits and harms of breast cancer screening:an independent review. Lancet 2012; 380; 1778 - 1786.
  4. McPherson K Screening for breast cancer - balancing the debate BMJ 2010; 340:c3106
  5. Beral V, Alexander M, Duffy S, et al The number of women who would need to be screened regularly by mammography to prevent one death from breast cancer J Med Screen 2011; 18: 210–12
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There is an ongoing debate about how many women are overdiagnosed because they have been to breast screening. Indeed, there is no agreement even on how overdiagnosis should be presented, in terms of which population to report it from.

It has been shown there are at least eight different ways of presenting overdiagnosis estimates,[1] and this variety has contributed to the confusion about the level of overdiagnosis.

Two methods of presentation, which make particular intuitive sense, are:

  • the proportion of cancers diagnosed over the lifetime because of breast screening – this represents the additional burden caused by breast screening and is perhaps the most useful figure from a public health perspective
  • the proportion of cancers diagnosed during the screening period – this represents the probability of a cancer diagnosed being an overdiagnosis and is perhaps most useful from an individual woman’s perspective.

Overdiagnosis can be calculated by comparing a screened population with an unscreened population. This can be achieved by evaluating:

  • two areas of the same country, one with and one without screening,
  • different age groups, some which have experienced screening or not,
  • the same area before and after screening.

However, the risk of breast cancer varies between populations and none of these methods can guarantee that the risk of breast cancer in the comparison population is the same as the screened population, and adjusting for differences in risk is difficult.[2]

Estimates of overdiagnosis for invasive breast cancer range from −4% to 7% of invasive breast cancer incidence in the unscreened population for women aged 40 to 49 years, 2% to 54% for women aged 50 to 59 years, and 7% to 21% for women aged 60 to 69 years.[2]

The variation in both the presentation and the methodology used to calculate the estimates of overdiagnosis arises partly because the randomised control trials were not set up to measure overdiagnosis as an outcome. Also, in many of the trials, the control group also received screening after a number of years.

Of the trials given in our benefits: mortality reduction section, only three didn’t screen the control group at the end of the intervention period. It is possible to use these trials in order to estimate overdiagnosis in a screened versus non-screened setting. The proportion of overdiagnosed cancers changes under different definitions. In each case the numerator – the additional cancer cases in the screened group over the control group after long term follow-up – remains the same and the population used for the denominator varies.

The Proportion of Overdiagnosed Cancers in Three Randomised Control Trials Using Three Different Denominators

Definition Used Malmo I (55-69) Canada I Canada II
Excess cancers as a proportion of cancers diagnosed over whole follow up period in women invited for screening. 10.5% (82/780) 12.4% (82/663) 9.70% (67/693)
Excess cancers as a proportion of cancers diagnosed during screening period in women invited for screening. 18.7% (82/438) 22.7% (82/361) 16.0% (67/420)
Excess cancers as a proportion of cancers detected at screening in women invited for screening. 29.1% (82/282) 29.4% (82/279) 19.8% (67/338)

Adapted from the Independent Panel on Breast Screening.[3]

Overdiagnosis as a proportion of cancers diagnosed over the lifetime because of breast screening varies between 10 to 12% and between 19 and 23% as a proportion of all cancers diagnosed during the screening period.

References

  1. de Gelder R, Heijnsdijk E.A, et al Interpreting overdiagnosis estimates in population-based mammography screening Epidemiol Reviews, 2011, 33(1):111-121
  2. Biesheuvel C, Barratt A, Howard K, et al Effects of study methods and biases on estimates of invasive breast cancer overdetection with mammography screening: a systematic review Lancet Oncol 2007;8:1129-38
  3. Independent UK Panel on Breast Cancer Screening. The benefits and harms of breast cancer screening:an independent review. Lancet 2012; 380; 1778 - 1786.
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The wide variation in the estimates for both the benefits and harms have led to an inevitably wide range of estimates of the ratio of the number of women overdiagnosed to the number of lives saved. These range from 10 overdiagnosed cases for every death prevented to one overdiagnosed case for every two deaths prevented, reflecting a twenty-fold difference.[1,2]

In October 2011, Professor Sir Mike Richards, National Clinical Director for Cancer, and Dr Harpal Kumar, Chief Executive Officer of Cancer Research UK, asked Professor Sir Michael Marmot (Professor of Epidemiology and Public Health and Director of the Institute of Health Equity at University College, London) to convene and chair an Independent Panel to review the evidence on benefits and harms of breast screening in the context of the UK breast screening programmes.[3,4]

After reviewing the evidence, the Panel took the assumption that UK women aged 55 to 79 invited to breast screening had a 20% relative reduction in the risk of dying from breast cancer per year, compared with unscreened women. Because breast screening programmes in the UK had been established for more than twenty years they assumed that the benefit of breast screening has already accrued and so instead of reducing the current mortality rate by 20%, they calculated what the mortality rates would have been had there been no screening programme. They did this by increasing the current mortality rate by 25% (equivalent to a fall of 20% from the higher level). This provides an absolute reduced risk of 43 deaths prevented per 10,000 women invited to screening.

The panel were, however, clear that considerable uncertainty surrounds this estimate. The main types of uncertainty are:

  • statistical - the 95% confidence interval around the relative risk reduction of 20% is 11% to 27%,
  • bias - there are a number of potential sources of distortion in the trials which could have affected the estimates of the mortality benefits, and
  • relevance of the findings of these old trials to the current screening programmes.

To calculate the magnitude of overdiagnosis in women, UK screening programmes require information on women who have been in a screening programme from age 50-70, then followed for the rest of their lives, which is not available. Any estimate of this will, therefore, include uncertainty. Having reviewed the evidence, the Panel assumed an absolute risk of overdiagnosis of 19% and then applied this to the risk of being diagnosed with breast cancer per year in UK women aged 50 to 69 invited to breast screening. This provides an absolute risk of 129 women being overdiagnosed per 10,000 women invited to screen.

The Independent Panel, therefore, concluded that the Breast Screening Programmes in the UK extend lives but at a cost. The Review estimated that while breast screening prevents around 1,300 breast cancer deaths in the UK per year, but it can also lead to around 4,000 women each year aged 50 to 70 in the UK having treatment for a condition that would never have caused them harm.

Comparison of the Benefits and Harms of Breast Screening, in numbers

Measure Screening Benefits Screening Harms
Relative Risks Women invited for breast screening have a 20% reduced chance of dying per year in UK women aged 55 to 79 from breast cancer compared with what it would be without a screening programme. 19% of breast cancers diagnosed in women aged 50 to 70 invited for screening would not have caused any problem if left undiagnosed and untreated.
Number of deaths prevented and women overdiagnosed per year in the UK 1,307 3,971
Number of deaths prevented and women overdiagnosed per 10,000 invited to screening 43 (0.43%) deaths prevented 129 (1.29%) women overdiagnosed
Number of deaths prevented and women overdiagnosed per 10,000 who actually attended screening 56 deaths prevented 168 women overdiagnosed
Ratio of overdiagnosis to deaths prevented 1 death prevented 3 women overdiagnosed

References

  1. Gøtzsche PC, Nielsen M Screening for breast cancer with mammography Cochrane Database System Reviewed 2011
  2. Duffy SW, Tabar L, Olsen AH, et al Absolute numbers of lives saved and overdiagnosis in breast cancer screening, from a randomized trial and from the Breast Screening Programme in England J Med Screen 2010; 17: 25–30
  3. Independent UK Panel on Breast Cancer Screening. The benefits and harms of breast cancer screening:an independent review. Lancet 2012; 380; 1778 - 1786.
  4. Independent UK Panel on Breast Cancer Screening Independent Breast Screening Review. November 2012
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The figures obtained from breast screening refer to women invited to screening as the analysis is based on intention to treat. Analysis based on intention to treat minimises the impact on study results if drop-out rates differ between the groups being compared. Intention to treat analysis is useful for assessing the effect of a policy, rather than the effect of a treatment. Because women receive no benefit from receiving an invite to screening alone, both the benefit and harms associated with screening only accrue to women who actually attend screening. The risk reduction and the rate of women overdiagnosed will therefore be higher in women attending screening than in women invited to screen.

The absolute reduction in risk of dying from breast cancer for women attending screening can be estimated as the absolute risk reduction in those invited to screening (0.43%), divided by the average coverage rate in the NHSBSP (77%): 0.43% / 0.77 = 0.56% or 56 breast cancer deaths prevented per 10,000 women attending screening.

A similar calculation can be applied to the percentage of women with an overdiagnosis, so 1.29% / 0.77 = 1.68% or 168 per 10,000 women attending screening.

The same calculation can not simply be repeated for the number of cancers diagnosed, because another factor – affluence of the population – interacts with the variables involved: the risk of breast cancer increases in more affluent populations, and more affluent women are more likely to attend breast screening.[1,2] If on that basis, we assume the risk of breast cancer in women that attend breast screening is 10% higher than in women invited to screening then there will be 681 plus 10% (749) breast cancers diagnosed in 10,000 women attending screening.

Under this assumption then, after 20 years amongst 10,000 women who have attended screening:

  • 749 women will be diagnosed with breast cancer, and receive treatment.

Of these 749 women:

  • 157 will die from breast cancer, 56 fewer than in the group not attending screening.

Of the 592 who survive:

  • 56 will have their life saved by screening, see calculation above.
  • 168 will be diagnosed with a cancer and treated for a cancer that wouldn’t have caused problems in their lifetime (‘overdiagnosed’), see calculation above.
  • 369, the remainder, will be diagnosed with and treated for a cancer that would have been picked up without screening.

If the same 10,000 women were not able to attend screening, then after 20 years:

  • 582 will be diagnosed with breast cancer, and receive treatment, i.e. the 749 minus the number of overdiagnosed cases,
  • 168 women will have a breast cancer they never know about and that will not cause any harm during their lifetime.

Of the 582 women diagnosed:

  • 213 women will die from breast cancer, 56 more than in the group attending screening
  • 369, the remainder, will be treated for cancer and survive.

These figures have been illustrated in the infographic that explains the results of the breast screening independent review.

References

  1. National Cancer Intelliegence Network Cancer incidence by deprivation England, 1995-2004. 2008
  2. Maheswaran R, Pearson T, Jordan H, Black D Socioeconomic deprivation, travel distance, location of service, and uptake of breast cancer screening in North Derbyshire, UK J Epidemiol Community Health. 2006: 60(3):208-12.
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Women in the UK are invited to have breast screening every three years.[1,2]

A randomised controlled trial (RCT) Open a glossary item reported that increasing the screening interval from once every three years to once every year did not significantly decrease the predicted risk of dying from breast cancer within 15 years.[3] The trial ran over a period of seven years, and included around 76,000 women aged 50-62 at enrollment.[3] In an average 13.5 years of follow-up, no significant differences in actual mortality risk between the annual screening group and the three-yearly screening group were observed, confirming the trial predictions.[4] In most European countries the screening interval is two years.[3,5]

Interval cancers

Cancers may be diagnosed in the years between routine breast screens (interval cancers), either through failure to detect an abnormality at the time of screening (false negative result),or as a new event after a negative screen (true interval cancer). With less frequent screening, the number of true interval cancers will be higher.

If the incidence rate of interval breast cancer in the screened population is similar to the incidence rate of breast cancer in the unscreened population, then screening has minimal benefit. So the NHS Breast Screening Programme (NHSBSP) sets thresholds for the incidence of interval cancer: 1.2 cases per 1,000 women in year 1 or 2 of the 3-year interval, and 1.4 per 1,000 women in year 3.[6] Observed rates were 0.55 cases per 1,000 women in year 1; 1.13 in year 2; and 1.22 in year 3, in the UK (excluding Scotland) in women screened between 1997 and 2003, aged 50-64 at their last screen.[7]

References

  1. UK National Screening Committee. UK Screening Portal: Breast screening across the UK. 2012.
  2. NHS Breast Screening Programme. Accessed October 2012.
  3. Breast Screening Frequency Trial Group. The frequency of breast cancer screening: results from the UKCCCR Randomised Trial. United Kingdom Co-ordinating Committee on Cancer Research. Eur J Cancer. 2002;38(11):1458-64.
  4. Duffy S, Blamey RW, for the UKCCCR Breast Cancer Frequency Trial Group. O-1 Long-term mortality results from the UK Breast Screening Frequency Trial. European Journal of Cancer Supplements. 2007; 5(3):1.
  5. von Karsa L, Anttila A, Ronco G, Ponti A, Malila N, Arbyn M et al (2008). Cancer screening in the European Union: Report on the implementation of the Council Recommendation on cancer screening, First Report. Brussels: European Commission.
  6. Patnick J, Carrigan C. Audit of breast cancers in women aged 50 to 74. NHSBSP Publication No 62. Sheffield: NHS Cancer Screening Programmes. 2006.
  7. Bennett RL, Sellars SJ, Moss SM. Interval cancers in the NHS breast cancer screening programme in England, Wales and Northern Ireland. Br J Cancer. 2011;104(4):571-7.
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Screening test accuracy is a function of both sensitivity and specificity. Sensitivity is the ability to detect true positives (where a tumour exists and is identified on mammogram) and true negatives (where no tumour exists and no tumour is identified on mammogram). Specificity is the ability to exclude false positives (where no tumour exists but one is indicated on mammogram) and false negatives (where a tumour is present but missed on mammogram).

The sensitivity (true positive rate) of screening mammography was estimated in a meta-analysis Open a glossary item to be between 83% and 95%,[1] with a range of 39% to more than 90% in an International Agency for Research on Cancer (IARC) review.[2] The specificity of screening mammography exceeds 80%, with many studies showing specificity above 95%.[1,2] However, these estimates are based on data published before 2002, therefore their relevance to current mammography methods is unclear.

Mammography is around 10% less sensitive in women under 50 than in women aged 50-59, the meta-analysis showed.[1] This is because younger women have more dense breast tissue, making their mammograms harder to read. Women in their 40s screened within the UK Age Trial had a 5% risk of a false-positive result at their first screen.[3]

Around 1 in 13 (7.7%) women in the NHSBSP in England were recalled for further tests after their first mammogram, data for financial year (FY) 2010/11 show.[4] Around 1 in 10 (9.5%) of those women were diagnosed with cancer.[4] Recall rates are higher for first screens than subsequent ones, typically because unusual findings on first screens (which may be normal for the woman) are investigated in full.[5] This means the positive predictive value(PPV); the proportion of women with positive screening results who are diagnosed with cancer) is lower at first screens. At subsequent screens the previous investigations can be referred back to without needing to recall the woman, so only new unusual findings are investigated in full. This means the recall rate is lower at subsequent screens, but the PPV is higher. In FY2010/11 in England, around 1 in 34 (2.9%) women were recalled after a subsequent screen, and of those almost 1 in 4 (25.5%) were diagnosed with cancer.[4]

Number of views taken at mammography

Two-view mammography – in which one image is taken from above and one from the side for each breast – is used in all the national breast screening programmes across the UK.[6]

When the NHSBSP began in England, single view mammogram (from the side) was used. In 1995, two-view mammography was introduced for all first (prevalent) screens, after an RCT showed a 24% increase in cancer detection rates and a 15% decrease in recall rates for two-view versus single-view at this first screen.[7] In 2003, two-view mammography was extended to all subsequent (incident) screens in England, after research showed that two-view mammograms were particularly effective in detecting small invasive cancers.[8] In Northern Ireland, two-view mammograms have been used at all screens since the programme started.[9] Two-view mammography at every screen was implemented in Wales in 2001, and in Scotland between 2008-2009.[10,11]

Digital mammography

Digital mammography is being introduced into the UK breast screening programmes, with equipment in at least 85% of screening units.[12] Cancer detection rates are slightly higher with digital mammography than conventional film mammography, with no detectable impact on recall rates or PPV, a meta-analysis showed.[13]

Double-reading and computer-aided diagnosis

In the majority of UK breast screening units, mammograms are read by two people (double-reading): either two radiologists, or a radiologist and an experienced radiographer.[14,15] In some units, mammograms are read by two experienced radiographers and a radiologist is consulted if the radiographers disagree.[14] Double-reading increases cancer detection rates by 10% in comparison with reading by one person, a meta-analysis showed.[16] Computer-aided diagnosis (in which a single human reader uses a computer programme designed to bring his/her attention to suspicious features) is the subject of ongoing research, but the evidence is presently inconclusive.[17]

HRT and mammography

Users of hormone replacement therapy (HRT) are more likely than HRT non-users to receive false negative or false positive screening results, a systematic review and large cohort studies have found.[18-20] This may be because HRT increases breast density, making mammograms harder to read.[19]

Sensitivity was 83% in current HRT users versus 92% in never-users; and specificity was 97% in current users versus 98% in never users, the UK Million Women study found.[19] Current users were 46% more likely than never users to receive a false positive recall, and past users were 12% more likely, a meta-analysis showed.[21]

References

  1. Mushlin AI, Kouides RW, Shapiro DE. Estimating the accuracy of screening mammography: a meta-analysis. Am J Prev Med. 1998 ;14(2):143-53.
  2. International Agency for Research on Cancer/World Health Organization (IARC/WHO). IARC Handbooks of Cancer Prevention: Breast Cancer Screening. Geneva: IARC Press, 2002.
  3. Johns LE, Moss SM; Age Trial Management Group. False-positive results in the randomized controlled trial of mammographic screening from age 40 ("Age" trial). Cancer Epidemiol Biomarkers Prev. 2010;19(11):2758-64.
  4. National Health Service Breast Screening Programme. Breast screening programme- England, 2010-11. March 2012.
  5. National Health Service Breast Screening Programme. NHS Breast Screening . 2012.
  6. UK National Screening Committee. UK Screening Portal: Breast screening across the UK. 2012.
  7. Wald NJ, Murphy P, Major P, Parkes C, Townsend J, Frost C. UKCCCR multicentre randomised controlled trial of one and two view mammography in breast cancer screening. BMJ. 1995;311(7014):1189-93.
  8. Blanks RG, Moss SM, Wallis MG. Use of two view mammography compared with one view in the detection of small invasive cancers: further results from the National Health Service breast screening programme. J Med Screen. 1997; 4(2): 98-101.
  9. Bennett RL, Blanks RG, Patnick J, Moss SM. Results from the UK NHS breast screening programme 2000–05. J Med Screen 2007;14:200–204.
  10. Breast Test Wales. The Report of the Director, 2005.
  11. Information Services Division (ISD) Scotland. Scottish Breast Screening Programme, 2012.
  12. NHS Breast Screening Programme. Digital mammography. 2012.
  13. Vinnicombe S, Pinto Pereira SM, McCormack VA et al. Full-field digital versus screen-film mammography: comparison within the UK breast screening program and systematic review of published data. Radiology. 2009 May;251(2):347-58.
  14. NHS Breast Screening Programme. NHS Breast Screening Programme: Annual Review 2011. Sheffield: NHS Breast Screening Programme. 2011.
  15. Advisory Committee on Breast Cancer Screening (2006). Screening for Breast Cancer in England: Past and Future. NHSBSP Publication No. 61. Sheffield: NHS Cancer Screening Programmes.
  16. Taylor P, Potts HW. Computer aids and human second reading as interventions in screening mammography: two systematic reviews to compare effects on cancer detection and recall rate. Eur J Cancer. 2008;44(6):798-807.
  17. Azavedo E, Zackrisson S, Mejàre I, Heibert Arnlind M. Is single reading with computer-aided detection (CAD) as good as double reading in mammography screening? A systematic review. BMC Med Imaging. 2012;12:22.
  18. Banks E. Hormone replacement therapy and the sensitivity and specificity of breast cancer screening: a review. J Med Screen. 2001;8(1):29-34.
  19. Banks E, Reeves G, Beral V et al. Influence of personal characteristics of individual women on sensitivity and specificity of mammography in the Million Women Study: cohort study. BMJ. 2004;329(7464):477.
  20. Crouchley K, Wylie E, Khong E. Hormone replacement therapy and mammographic screening outcomes in Western Australia. J Med Screen. 2006;13(2):93-7.
  21. Banks E, Reeves G, Beral V et al. Hormone replacement therapy and false positive recall in the Million Women Study: patterns of use, hormonal constituents and consistency of effect. Breast Cancer Res. 2006;8(1):R8.
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All women aged 50-70 are routinely invited to attend breast screening throughout the UK. In England a trial is taking place to look at the possible benefits of extending breast screening so that women aged 47-50 and 70-73 are also invited.[1,2]

The eligible age group for breast screening was originally 50-64 in all the UK countries. This was extended to age 70 first in England in 2002, then in Scotland in 2003-2004, Wales in 2006, and Northern Ireland in 2009.[3-57]

Women over 70

Women beyond routine screening age can still receive three-yearly mammograms on request. However, only around half of women in this age group are aware they can request a mammogram, a study showed.[8] Accordingly, in 2005-2008 (before the extension to age 73 began) only 4% of women over 70 in England were screened (following self-referral), compared with 72% of women aged 65-70 (following routine invitation).[9] Self-referral to screening among women over 75 was particularly low in this period – only 2% of this group were screened.[9] The National Early Diagnosis Initiative (NAEDI) is examining ways to increase breast cancer awareness and promote earlier diagnosis in older women.

Women under 50

Inviting women to annual screening from age 39-41 onwards did not significantly reduce their risk of dying from breast cancer within 5-15 years, an RCT of around 161,000 women in Great Britain (the Age Trial) showed.[10] The participants of this study have now joined their national routine screening programmes, and will be followed-up until at least age 60 to determine the long-term impact of screening at an earlier age.[11] Meta-analyses of all published trials worldwide report that screening women aged 39-49 reduces their risk of breast cancer death by 15%-17%, but it remains unclear how much of this effect is due to routine screening after age 50.[12,13]There are various risks of screening younger women, including false-positive results and anxiety caused by them, possible over-diagnosis (identifying and treating early-stage cancers which may have never have manifested symptoms), and radiation from the additional mammograms.[14,15] Many of these factors will be considered in the Age Trial follow-up.[11]

Women under 50 with an increased risk of breast cancer

Women who have an increased risk of developing breast cancer, but are too young to join the national screening programmes, are offered annual screening using mammography and/or magnetic resonance imaging (MRI) Open a glossary item.

These women may have a genetic predisposition to developing breast cancer (usually identified because of a family history of the disease), or may have an increased risk because of previous medical treatment (for example radiotherapy to the chest before age 25).[16] Women in these circumstances are referred for screening by their genetics service or oncologist.[17] Some remain on the higher-risk screening programme past age 50, whilst others join the national screening programme at age 50.[16,17]

References

  1. Moser K, Sellars S, Wheaton M et al. Extending the age range for breast screening in England: pilot study to assess the feasibility and acceptability of randomization. J Med Screen. 2011;18(2):96-102.
  2. The Information Centre for Health and Social Care. Breast cancer: women screened under national programme rises to 1.9 million in 2010-11. Accessed October 2012.
  3. Breast Test Wales. The Report of the Director, 2005.
  4. Information Services Division (ISD) Scotland. Scottish Breast Screening Programme, 2012.
  5. Advisory Committee on Breast Cancer Screening (2006). Screening for Breast Cancer in England: Past and Future. NHSBSP Publication No. 61. Sheffield: NHS Cancer Screening Programmes.
  6. Northern Ireland Public Health Agency. Northern Ireland Breast Screening Programme: Annual Report and Statistical Bulletin 2009-2010. Belfast: Public Health Agency Quality Assurance Reference Centre, 2012.
  7. Northern Ireland Executive. Health Minister announces extension to NI breast cancer screening programme. Accessed October 2012.
  8. Collins K, Winslow M, Reed MW et al. The views of older women towards mammographic screening: a qualitative and quantitative study. Br J Cancer. 2010;102(10):1461-7.
  9. Bennett RL, Moss SM. Screening outcomes in women over age 70 who self-refer in the NHSBSP in England. J Med Screen. 2011;18(2):91-5.
  10. Moss SM, Cuckle H, Evans A et al. Effect of mammographic screening from age 40 years on breast cancer mortality at 10 years' follow-up: a randomised controlled trial. Lancet. 2006;368(9552):2053-60.
  11. Health Technology Assessment Programme. Details of HTA project in progress: Long-term follow up of a trial of annual mammographic screening from age 40. 2012.
  12. Nelson HD, Tyne K, Naik A et al. Screening for breast cancer: an update for the U.S. Preventive Services Task Force. Ann Intern Med. 2009;151(10):727-37, W237-42.
  13. Magnus MC, Ping M, Shen MM, Bourgeois J, Magnus JH. Effectiveness of mammography screening in reducing breast cancer mortality in women aged 39-49 years: a meta-analysis. J Womens Health (Larchmt). 2011;20(6):845-52.
  14. Moss S. Screening women aged 40-49 years . Prev Med. 2011;53(3):105-7.
  15. Armstrong K, Moye E, Williams S, Berlin JA, Reynolds EE. Screening mammography in women 40 to 49 years of age: a systematic review for the American College of Physicians. Ann Intern Med. 2007: 3;146(7):516-26.
  16. NHS Breast Screening Programme. High risk surveillance imaging protocols. 2012.
  17. NHS Breast Screening Programme. Breast screening for women with a higher risk of breast cancer. 2012.
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Women who receive a negative (no disease found) result on their mammogram report no related anxiety.[1] Anxiety in women who receive false positive results report is typically short-term, though for some of these women breast cancer-specific anxiety is increased in the longer term.[1-3] In women under 50, the anxiety associated with false positive results seems to have little effect on attendance rates for subsequent screens, but some studies of routine screening populations have reported an association.[1,3]

Women with a family history of breast cancer report similar levels of anxiety to women in the general population, in these situations.[4]

References

  1. Brett J, Bankhead C, Henderson B, Watson E, Austoker J. The psychological impact of mammographic screening. A systematic review. Psychooncology. 2005 Nov;14(11):917-38.
  2. Armstrong K, Moye E, Williams S, Berlin JA, Reynolds EE. Screening mammography in women 40 to 49 years of age: a systematic review for the American College of Physicians. Ann Intern Med. 2007: 3;146(7):516-26.
  3. Brewer NT, Salz T, Lillie SE. Systematic review: the long-term effects of false-positive mammograms. Ann Intern Med. 2007 Apr 3;146(7):502-10.
  4. Watson EK, Henderson BJ, Brett J, Bankhead C, Austoker J. The psychological impact of mammographic screening on women with a family history of breast cancer--a systematic review. Psychooncology. 2005 Nov;14(11):939-48.
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In FY2009/10, around 3,100 in situ and micro-invasive breast tumours in women aged 50-70 were detected by the national screening programmes in the UK.[1]This represents around 20% of all screen-detected breast tumours in this period.[1] Around eight in ten in situ breast tumours in this age group in FY2009/10 were detected through screening.[2-5]

The natural history of in situ breast carcinoma is not fully known, but there is evidence it carries a raised risk for developing invasive breast cancer, and sometimes it is thought of as being pre-invasive disease or an “early breast cancer”.[6] Almost all (99%) of the in situ tumours detected in the NHS Breast Screening Programme (NHSBSP) in FY2009/10 were surgically treated, with the proportion receiving lumpectomy (72%) similar to the invasive tumours, and the proportion receiving mastectomy (27%) slightly higher.[1]

The Sloane project began in 2003 to improve understanding of the natural history and optimal treatment of in-situ breast tumours.[7] More than 80 UK breast screening units participate in the Sloane project, providing data on around 11,000 in situ tumour patients to date.[8]

References

  1. NHS Breast Screening Programme. NHS Breast Screening Programme: Annual Review 2011. Sheffield: NHS Breast Screening Programme. 2011.
  2. Data were provided by the Office for National Statistics on request, June 2012. Similar data can be found here: http://www.ons.gov.uk/ons/search/index.html?newquery=cancer+registrations
  3. Data were provided by ISD Scotland on request, April 2012. Similar data can be found here: http://www.isdscotland.org/Health-Topics/Cancer/Publications/index.asp#605
  4. Data were provided by the Welsh Cancer Intelligence and Surveillance Unit on request, April 2012. Similar data can be found here:http://www.wales.nhs.uk/sites3/page.cfm?orgid=242&pid=51358
  5. Data were provided by the Northern Ireland Cancer Registry on request, June 2012. Similar data can be found here: http://www.qub.ac.uk/research-centres/nicr/CancerData/OnlineStatistics/
  6. Robinson D, Holmberg L, Moller H. The occurrence of invasive cancers following a diagnosis of breast carcinoma in situ. Br J Cancer 2008.99(4):611-15.
  7. West Midlands Cancer Intelligence Unit and NHS National Screening Programmes.The Sloane Project. 2012.
  8. West Midlands Cancer Intelligence Unit and NHS National Screening Programmes.The Sloane Project Newsletter, Issue 3 February 2012. 2012.
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