PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
- Breast cancer is the most common malignant disease diagnosed in women worldwide.
- Mammography is a special type of low-dose X-ray imaging of the breast to create detailed soft tissue images.
- A digital mammography system usually requires a lower radiation dose than film screen mammography for the same image quality. Digital detector converts the X-ray photons to an electronic signal, which is further processed and displayed as a greyscale image.
- The digital system provides greater contrast resolution and thus better visualisation of skin, peripheral breast tissue, and breast density. Besides this, it allows for changes in zoom, contrast and brightness, which increase the ability to detect subtle abnormalities.
- It is used for screening in asymptomatic women for early detection of breast cancer.
- It is also used diagnostically in symptomatic women.
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Screening with mammography has the ability to detect breast cancer at an early stage. Around a third of breast cancers in the UK are now diagnosed through screening.
- The purpose of screening mammography is to reduce mortality from breast cancer without increasing mortality from other diseases.
- The programmes for breast screening differ in the UK. It is offered:
- In England, Scotland and Ireland to women aged 50-70 years every three years.
- In Wales to women aged 50-64 years every two years.
- The programme in England is now phasing in an extension of the age range of women eligible for breast screening to those aged 47 to 73. This started in 2010 and is expected to be complete by 2016.
- This means that all women in England will receive two extra screening invitations in their lifetime. It also means that all women will receive their first screening invitation by their 50th birthday.
- Recall of all patients with abnormalities is usually to specialised assessment units. These allow further investigation, often with:
- Clinical examination.
- Special view mammography.
- Ultrasound examination (useful in younger patients and to identify cysts particularly).
- Fine-needle aspiration and cytology.
- However, around 80% of women who are recalled for assessment following an abnormal mammogram do not have breast cancer.
- Certain high-risk groups of women are recommended to have more frequent mammograms and/or MRI scans or ultrasound scan than the screening programme. Such groups include:
- Patients who have had breast cancer.
- Patients who have a strong family history of breast cancer.
- Patients who have a relevant genetic history.
- The role of MRI for breast cancer screening is still evolving. Currently, MRI screening, in combination with mammography, is usually reserved to the screening of high-risk patients.
- Supporters of adjunct ultrasonography to the screening regimen for breast cancer argue that it is a safe and inexpensive approach to reduce the false negative rates of the screening process. However, there is no methodologically sound evidence available justifying the routine use of ultrasonography as an adjunct screening tool in women at average risk for breast cancer.
Preparing patients for a mammogram
Most specialised breast screening units will have a specific referral form requesting relevant information and with diagrams to assist description of examination findings. These include information on:
- Urgency of the referral.
- Breast symptoms, including lumps, pain, discharge.
- Breast examination findings, including lumps (diagram to show size, position, consistency).
- Lymph node examination, particularly axillary.
- Relevant past history of any breast disease, both benign and breast cancer.
- Women with breast reconstructions with no underlying breast tissue do not require mammographic screening, whereas women with breast augmentations performed with implants do require routine screening to evaluate the native breast tissue.
- Note that although breast implants can sometimes impede accurate mammography it is still possible to perform mammography in patients with implants.
- Menstrual history.
- Medication - especially any hormones.
- Family history - particularly of breast cancer.
Advice to patients
- Do not wear talcum powder or deodorant, as these can produce calcium spots and affect the quality of the image.
- Any previous mammograms should be made available to the radiologist to help interpretation.
- Ensure that instructions on notification of results are clear and understood.
- Explanation of the procedure. This should include a brief description of what is involved. It can involve discomfort because of the compression of the breast tissue between plastic paddle and platform. If necessary, less compression can be used to reduce discomfort.
The benefits of the screening programme
The best evidence for the relative benefit of screening on mortality reduction comes from 11 randomised controlled trials of breast screening. Meta-analysis of these trials with 13 years of follow-up estimated a 20% reduction in breast cancer mortality in women invited for screening. The relative reduction in mortality will be higher for women actually attending screening but by how much is difficult to say because women who do not attend are likely to have a different background risk.
For the UK screening programmes, this currently corresponds to about 1,300 deaths from breast cancer being prevented each year, or equivalently about 22,000 years of life being saved.
However, a Cochrane review has found that breast cancer mortality was actually an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death. Some trials with adequate randomisation did not find an effect of screening on total cancer (including breast cancer) mortality after ten years or on all-cause mortality after thirteen years.
Limitations of the screening programme
Mammography has long been the mainstay of breast cancer detection and is the only screening test proven to reduce mortality. Although it remains the gold standard of breast cancer screening, there is increasing awareness of sub-populations of women for whom mammography has reduced sensitivity. Mammography also has undergone increased scrutiny for false positives and excessive biopsies, which increase radiation dose, cost, and patient anxiety.
In radiographically dense breasts, non-calcified breast cancers are more likely to be missed than in fatty breasts. As a consequence, some cancers are not detected by mammography screening.
In screening mammography, the most serious concern is the risk of overdiagnosis - that is, diagnosis of breast cancer that would in the absence of screening not have led to clinically manifest disease in the woman’s lifetime.
Overdiagnosis in screening mammography is a widely debated topic and most studies in this area have major methodological limitations. One study has demonstrated that overdiagnosis of breast cancer amounted to 2.3% in screen-targeted women.
A recent Cochrane review has demonstrated that for every 2,000 women invited for screening throughout ten years, one will avoid dying of breast cancer and ten healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily.
In addition, more than 10% of women with abnormal mammograms will experience significant psychological distress, including anxiety and uncertainty, for years because of false positive findings. The breast cancer specific psychological distress may last for up to three years, and may even reduce the likelihood that women will return for their next round of mammography screening.
The Nordic Cochrane Centre has written an evidence-based leaflet for lay people that is available in several languages. This has been written to ensure that the women are fully informed before they decide whether or not to attend screening. Although the new breast cancer screening leaflet for UK women was updated in 2013, many experts feel that it still fails to spell out the true risks of mammography and therefore denies women the chance to make a properly informed choice.
Putting together benefit and overdiagnosis, the Independent UK Panel on Breast Cancer Screening estimates that for 10,000 UK women invited to screening from age 50 for 20 years, about 681 cancers will be found of which 129 will represent overdiagnosis, and 43 deaths from breast cancer will be prevented. In round terms, therefore, for each breast cancer death prevented, about three overdiagnosed cases will be identified and treated.
In the future it is likely that optimal breast cancer screening will ultimately require a personalised approach based on individual cancer risk with selective application of specific screening technologies best suited to the individual's age, risk, and breast density.
Further reading & references
- Improving Outcomes: A Strategy for Cancer; Dept of Health, January 2011
- Bond M, Pavey T, Welch K, et al; Systematic review of the psychological consequences of false-positive screening mammograms. Health Technol Assess. 2013 Mar;17(13):1-170, v-vi. doi: 10.3310/hta17130.
- Familial breast cancer: Classification and care of people at risk of familial breast cancer and management of breast cancer and related risks in people with a family history of breast cancer; NICE Clinical Guideline (June 2013)
- Gartlehner G, Thaler K, Chapman A, et al; Mammography in combination with breast ultrasonography versus mammography for breast cancer screening in women at average risk. Cochrane Database Syst Rev. 2013 Apr 30;4:CD009632. doi: 10.1002/14651858.CD009632.pub2.
- Marmot MG; Sorting through the arguments on breast screening. JAMA. 2013 Jun 26;309(24):2553-4. doi: 10.1001/jama.2013.6822.
- The benefits and harms of breast cancer screening: an independent review; Lancet. 2012 Nov 17;380(9855):1778-86. doi: 10.1016/S0140-6736(12)61611-0. Epub 2012 Oct 30.
- Gotzsche PC, Jorgensen KJ; Screening for breast cancer with mammography. Cochrane Database Syst Rev. 2013 Jun 4;6:CD001877. doi: 10.1002/14651858.CD001877.pub5.
- Drukteinis JS, Mooney BP, Flowers CI, et al; Beyond mammography: new frontiers in breast cancer screening. Am J Med. 2013 Jun;126(6):472-9. doi: 10.1016/j.amjmed.2012.11.025. Epub 2013 Apr 3.
- Njor SH, Olsen AH, Blichert-Toft M, et al; Overdiagnosis in screening mammography in Denmark: population based cohort study. BMJ. 2013 Feb 26;346:f1064. doi: 10.1136/bmj.f1064.
- Screening for Breast Cancer with Mammography; The Nordic Cochrane Centre, 2012
- The Benefits and Harms of Breast Cancer Screening: An Independent Review - The Independent UK Panel on Breast Cancer Screening; Cancer Research UK and the Dept of Health (England), October 2012
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Richard Draper
Dr Louise Newson
Prof Cathy Jackson