Behind The Medical Headlines

Screening for breast cancer

• Ms EDC Anderson, Consultant Surgeon, Edinburgh Breast Unit and Clinical Director of Southeast Scotland Breast Screening Centre, Edinburgh, Scotland

Summary

There is a battlefield of scientific literature debating the value of breast screening. How effective is breast screening and who should be screened? Ms Elaine Anderson provides a review of the evidence and the outcomes of the NHS breast screening programme in the UK.

Declaration of interests: No conflict of interests declared

In 1986, the Forrest Report recommended that breast screening should be introduced for all women between the ages of 50 and 64 in the UK.¹ Whilst women over the age of 64 were also to be eligible for screening, it was decided that these women should initiate their own invitations for screening due to poor compliance in Swedish studies of women in this age group.² The method of screening to be used was to be a single oblique mammogram at an interval of three years. Subsequent research has shown that 2-view mammography at the time of first screen can improve sensitivity, i.e. number of cancers detected (24%), and reduce the number of benign recalls by 15%.³

There is now a battlefield of literature debating the value of breast screening. Review of currently published data on the effect of breast screening, including the large randomised trials (Swedish Two Counties and the Health Insurance Plan (HIP) project) suggests that a reduction in breast cancer deaths in the order of 21-35% at five years should be expected for women over the age of 50.^2,4,5,6,7,8 The robustness of the evidence confirming the value of breast screening in reducing breast cancer deaths was confirmed by the International Agency for Research on Cancer (IARC), who convened an international panel of 24 experts from 11 countries to report on this matter. The working group concluded that the reduction in mortality from breast screening in women who participate in screening programmes is around 35%. The working group also found that many of the earlier criticisms were unsubstantiated and recognised that whilst there were some deficiencies in the published evidence these did not invalidate the trials’ findings.

In a UK context, this means that two women in every 1,000 screened would be saved over the next ten years. It is for the individual woman to decide whether screening is worthwhile. In women under the age of 50 a significant benefit is less clear.^2,6,9 In the high-risk younger population, cancer detection rates are similar to the National Heath Service Breast Screening Programme (NHSBSP), but there is no information on mortality reduction. Specific studies addressing this question are now being carried out.

In the UK, under the NHSBSP, women are invited for breast screening on a rotational basis to either static units in urban areas or mobile units in rural areas. In Scotland, mammograms are read independently by two experienced radiologists, increasing sensitivity by a further 10%.¹⁰ Around 5-7% of women are recalled for further evaluation, including clinical examination, further mammographic views and/or ultrasound. Recall may be associated with significant anxiety and it is important to keep recall rates to a minimum while optimising cancer detection rates. Approximately 1% of all women screened require multidisciplinary review, including surgical, radiological and pathological input. These women require a cytological/histological diagnosis before any definitive surgery; as about 60-80% of lesions are impalpable, fine needle aspiration (FNA) or core biopsy requires image guidance. This multidisciplinary approach is vital to optimise results in order to ensure that a high quality of programme-specific quality assurance (QA) guidelines for each stage of the screening procedure have been instituted (Figure 1).¹¹

There is continual improvement in performance in relation to cancer detection ratios, standarised detection ratios (SDR) and the proportion of small cancers diagnosed. Cancers now detected by breast screening account for one-third of the workload of new cancers detected in breast units. The proportion of self-referral in women aged 65 continues to increase. Recent studies in the UK show a higher compliance than originally shown from Swedish studies. Older women have a higher breast cancer risk (7/1,000 women screened), and extension of the age range of invitation in the screening programme to include women up to the age of 70 will be implemented in Scotland from April 2003.

The benefits of screening include the detection of cancers at an earlier stage in their life history, allowing improved survival and less radical treatment with more breast conservation. The radiation dose involved in mammography is very low (a rough estimate is that one excess cancer per two million screened may be caused after a lag phase of ten years), and even with cumulative doses the number of cancers detected far outweighs those induced by several orders of magnitude. The debate about the over diagnosis of special type cancers and ductal carcinoma in situ (DCIS) continues, and is based on our incomplete knowledge of their natural history and appropriate treatment.

Breast screening has significant financial implications, but, provided the QA is high, it remains cost-effective.

References

1. Hamilton T, Langlands AW, Prescott RJ. The treatment of operable cancer of the breast: a clinical trial in the South-East Region of Scotland. Br J Surg 1974; 61:758-61.
2. Veronesi U, Cascinelli N, Mariani L et al. Twenty year follow-up of a randomised study comparing breast-conserving surgery with radical mastectomy for early breast cancer. New Eng J Med 2002; 347:1227-32.
3. Fisher B, Anderson S, Bryant J et al. Twenty year follow-up of a randomised trial comparing total mastectomy, lumpectomy, and lumpectomy plus irradiation for the treatment of invasive breast cancer. N Eng J Med 2002; 347:1233-41.
4. Chetty U, Jack W, Prescott RJ et al. on behalf of the Edinburgh Breast Unit. Management of the axilla in operable breast cancer treated by breast conservation: a randomised clinical trial. Br J Surg 2000; 87:163-9.
5. Forrest AP, Everington D, Steele RJ et al. The Edinburgh randomised trial of axillary sampling, or clearing, after mastectomy. Br J Surg 1995; 82:1504-08.