Breast screening with mammography

What is breast screening?

Breast cancer is the most common cancer in the UK, with women having a 1 in 7 lifetime risk of developing the disease.¹

The breast screening process²

The NHS Breast Screening Programme in England was set up in 1988 and provides 3-yearly routine breast screening to women. Breast screening uses mammography to detect small changes in the breast before other symptoms or signs of breast cancer develop.

If breast cancer is found at an early stage, there is an increased chance of breast-conserving surgery and a better prognosis for long-term survival.

Invitations for routine mammography screening are sent out to women aged 50–70 years (from the age of 50 years up to their 71st birthday) in England, Northern Ireland, Scotland, and Wales.

In some circumstances, women outside of this age range are also screened as part of the programme either through self or GP referral, or they may be invited as part of a research trial. The AgeX trial has been looking at the effectiveness of offering some women one extra screen between the ages of 47–49 years and between the ages of 71–73 years.

Not every woman will receive an invitation as soon as she is in the screening age range, but she should receive her first invitation for routine screening within 3 years of her 50th birthday.

Women older than the maximum age for screening in their area are currently excluded from the routine screening programme, but can continue to receive breast screening by self-referral to a local breast screening service.

Women at increased risk of breast cancer (eg, strong family history) may be eligible for breast screening before the age of 50 years. See the article on Familial Breast Cancer.

Information on local breast cancer screening services in England, Wales, Scotland, and Northern Ireland (NI) are available from:

• Breast Screening Programme England.³

• Breast Test Wales.⁴

• Scottish Breast Screening Service.⁵

• Northern Ireland Breast Screening Programme.⁶

Around 80% of women who are recalled for assessment following an abnormal mammogram do not have breast cancer⁷ . Around 1-2 in 23 women having a mammogram are called back; some of these are for technical reasons.²

Other imaging and screening techniques are not currently used in the UK programme.

The role of MRI for breast cancer screening is still evolving. Currently, MRI screening, in combination with mammography, is usually reserved for the screening of high-risk patients.

A Cochrane review of mammography in combination with breast ultrasonography versus mammography for breast cancer screening in women at average risk concluded:⁸

• Based on one study in women at average risk of breast cancer, ultrasonography in addition to mammography leads to more screening-detected breast cancer cases.

• For women with dense breasts, cohort studies more in line with real-life clinical practice confirmed this finding, whilst cohort studies for women with non-dense breasts showed no statistically significant difference between the two screening interventions.

• However, the number of false-positive results and biopsy rates were higher in women receiving additional ultrasonography for breast cancer screening.

• None of the included studies analysed whether the higher number of screen-detected cancers in the intervention group resulted in a lower mortality rate compared to mammography alone.

Screening for breast cancer: benefit vs harm²

A 2013 Cochrane review concluded⁹ :

• Screening reduces mortality by around 15%, and overdiagnosis and over-treatment is around 30%.

• For every 2,000 women invited for screening over 10 years, one death from breast cancer will be prevented, 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 favour of screening.

Benefits of the breast screening programme

Early breast cancer detection
In 2020–21 in England:

• A total of 10,813 women aged 45 years and older had cancers detected by the screening programme, which represents a rate of 9.1 cases per 1000 women screened.

• Detection rates were lowest for women aged 45–49 years (6.4 women with cancer detected per 1000 women screened) and highest for women aged 75 years and older (22.3 women per 1000 women screened).

• Amongst the core programme (women aged 50 years to under 71 years), the detection rate was 8.9 per 1000 women screened.

• Of all women with cancers detected, 48.7% had invasive but small cancers (less than 15 mm in diameter), which are usually too small to detect by palpation on clinical examination.

Reduced breast cancer mortality
A meta-analysis in 2012 of 11 randomised trials showed that the relative risk of breast cancer mortality for women invited to screening compared with controls not invited was 0.80, which is a relative risk reduction of 20%.

Harms of the breast screening programme

Overdiagnosis
Overdiagnosis refers to the detection of low-risk or non-progressing breast cancers through screening that would not have been diagnosed without screening, and would not have been life threatening. A meta-analysis in 2012 showed that:

• For every 10,000 UK women aged 50 years invited to screening for the next 20 years, 129 cases of breast cancer (invasive and non-invasive) would be over-diagnosed, which equates to 19% of breast cancers in this group of women.

• Of the 307,000 women aged 50–52 years who are invited to begin screening each year, just over 1% would have an over-diagnosed cancer in the next 20 years.

If breast cancer is diagnosed through screening, treatment is recommended to all women to reduce the risks of recurrence and breast cancer mortality, as it is not possible to distinguish non-progressive from progressive disease, due to the lack of reliable prognostic markers. Breast cancer treatments, such as radiotherapy, chemotherapy, and hormonal treatments, may have associated risks.

False-positive mammograms
False-positive mammograms could lead to unnecessary further investigations, including clinical examination, further mammography, breast ultrasound, and fine-needle aspiration and/or biopsy.

A systematic review concluded that the experience of having a false-positive screening mammogram can cause breast cancer-specific psychological distress that may persist for up to 3 years and reduce the likelihood that women will return for their next round of mammography screening compared with women with normal mammogram results.

Other potential harms
Other potential harms include false reassurance due to missed cancer and incorrect diagnosis, and pain and discomfort during and after the mammogram procedure.

Recall for assessment, such as repeat mammography and/or ultrasound, is associated with significant anxiety, particularly as most women have had no previous indication of a breast problem.