Breast Cancer Screening

Breast Cancer is the most common cancer, with women having a 1 in 8 lifetime risk of developing the disease. Many trials have looked at whether screening has an impact on outcome in terms of mortality and morbidity. Several countries have set up screening programmes to call women for routine screening. Debate over the benefit, however, continues.

Screening for breast cancer: benefit v/s harm

The breast cancer-screening programme was set up to allow for the early detection and treatment of breast cancer in women. As evidence emerges from years of screening across several countries, debate continues about whether the benefit outweighs the negative effects.

An independent review in 2012 concluded:

Screening as currently performed gives a 20% relative risk reduction in mortality. For every 10,000 women aged 50 beginning the screening programme for the next 20 years, 43 deaths from breast cancer would be prevented, and 129 cases would be over diagnosed. This equates to one death prevented for every three cases over diagnosed.

A 2013 Cochrane review concluded: Screening reduces mortality by around 15%, and over-diagnosis and overtreatment is around 30%.

For every 2,000 women invited for screening over 10 years, one will avoid dying of breast cancer, and 10 healthy women will be treated unnecessarily. More than 200 women will experience psychological distress caused by false positive findings.

Breast cancer mortality in itself is an unreliable outcome measure, as it is biased in favor of screening.

The Canadian Task Force in 2011 found that mammography is associated with significant reductions in the relative risk of death from breast cancer in those aged 50-69 years. The benefits of mammography for women aged 60-69 years (number needed to screen (NNS) 432) are greater than for women aged 50-59 years (NNS 910). Screening about 720 women aged 50-69 years once every 2-3 years for about 11 years would prevent one death from breast cancer, but it would also result in about 204 women having a false positive result on a mammogram and 26 women having an unnecessary biopsy of their breast. However, a report on 25 years of breast screening in Canada in 2014 suggested for women aged 40-59 years having annual mammography, there was NO significant reduction in mortality.

For women aged 40-49 years there is only limited evidence of a reduction in mortality. This may be due to the difficulties in interpreting mammograms in premenopausal women, due to glandular breast tissue, and also to the lower incidence of breast cancer in this age group.

There is some evidence to suggest that reduction in mortality is independent of screening practice. Some analyses suggest there may be evidence to support an overall net harm for women screened.

There is evidence that women who have had false positive breast screening results may experience psychological distress, which may persist for up to three years, and reduce their likelihood of returning for their next screening test.

Women need to be informed of the risk of over-diagnosis but a recent small study suggested that this did not have much impact on their decision to have screening.

Population in mind

All women between the ages of 50 and 70 are invited to attend for screening every three years.

Women who have a family history of breast cancer should be referred for genetic testing and surveillance.

Otherwise, women who may be at higher risk of breast cancer – for example, no history of breast-feeding, having no children, having children at late ages (especially over 30), long-term hormone replacement therapy (HRT) use, obesity (for postmenopausal women only) and high consumption of alcohol – and advise them opportunistically of breast awareness.

Elements of screening

Screening takes place in the form of clinical examination and mammography. This allows small tumours to be detected before they are palpable. Since 2003, two images of each breast have been taken, craniocaudial, and mediolateral, and this increases the detection rate of even smaller abnormalities by up to 43%.