Issues around breast screening

A recent randomised controlled trial to evaluate the optimum screening interval compared annual mammography with three-yearly mammography over a period of seven years. Over 76,000 women were involved and the results showed that shortening the screening interval from the current three years did not produce a statistically significant decrease in the predicted mortality from breast cancer. 1 Therefore the screening interval in the Breast Screening Programme will remain at three years.

The NHSBSP has reviewed and refined its operation over the last twenty years based on research findings.1 Originally a single view mammogram was taken at each screen, but when a randomised controlled trial showed a 24% increase in cancer detection rates for two-view mammography at the first (prevalent) screen, this was introduced in 1995.2 Two-view mammography was extended to all screens in England from 2003 following new epidemiological evidence.3

It was also announced in 2000 that the upper age limit for inviting women for screening would be raised from 64 to 70 in England, Wales and Scotland. In England the programme will be extended further to cover women aged 47-73 by 2012.4 Older women can request screening and there is concern, that despite their higher risk of developing breast cancer, there is a lack of awareness amongst older women.5 Initiatives are underway to increase breast cancer awareness and promote earlier diagnosis in older women.6,7

The cost/benefit case for women younger than 47 receiving screening is under investigation.8,9 Younger women have denser breasts making cancer detection more difficult and there is also the associated risk from the additional radiation to be considered.10

All women, whatever their level of risk or age, need to be fully informed about their chance of developing breast cancer and the drawbacks, such as over-diagnosis and over-treatment, as well as the benefits of screening.15 A key element of the screening programme is the provision of quality-assessed information so that women can make an informed choice.16 New information leaflets are in preparation.

Annual screening using mammography or an MRI scan is available to young women aged under 50 with a family history of breast cancer if they are considered to be at moderate risk (17-30% lifetime risk) or high risk (>30% lifetime risk).11-13 Less than 1% of women are at high risk due to the inheritance of a faulty gene (BRCA1, BRCA2 and TP53), and after consultation with genetic counselling services, they may have risk-reducing surgery (prophylactic bilateral mastectomy).14

The NHSBSP continues to develop and explore better ways of delivering the service to maximise the benefits and minimise the drawbacks including false positive and false negative findings. Digital mammography, which has higher sensitivity (proportion with condition who test positive) for younger women and higher specificity (proportion without condition who test negative) than conventional mammography, is being introduced with the possibility of harnessing computers to help radiologists read the increasing number of mammograms.24,25

False positive results are an important problem as they cause anxiety and unnecessary additional assessments and may reduce attendance rates for subsequent screens.26,27 Around 9% of women are recalled after their first screen but less than 10% of these will have either an in situ or invasive cancer.28 At subsequent screens a lower percentage of women are recalled (around 4%) but a higher number (1 in 5) will have in situ or invasive cancer.28

Overall, around 95% of women attending screening have no abnormality and will be routinely invited for screening three years later. Of the 5% who are recalled, only 1 in 6 will have an in situ or invasive cancer.28 However, the chance of a recalled woman having cancer has risen since the introduction of two view mammography.29

Personal characteristics (use of HRT, previous breast surgery and BMI) may also affect the efficiency and possibly the effectiveness of mammography and need to be taken into consideration.30Acceptance rates are above the necessary 70% overall, but certain groups in the population, for instance minority ethnic women, have lower uptake, and strategies to encourage their attendance are being devised.

Some tumours detected by the screening programme are non-invasive in situ tumours, the main type being ductal carcinoma in situ (DCIS). The natural history of these tumours is not fully known but there is evidence that they carry a raised risk for invasive cancer,32 and sometimes they are thought of as being pre-invasive disease or an early cancer. Most DCIS tumours are treated in case they progress, inevitably leading to some over-treatment.23,31,32 To improve treatment for these non-invasive conditions and to help prevent over-treatment, a prospective study has been set up called the Sloane project.33,34

section updated 22/12/11