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What a mammogram is

A mammogram is an X-ray of the breast. The NHS breast screening programme uses mammograms to screen for breast cancer in women aged 50 to 70. In England, they are currently expanding the screening age from 47 to 73. After the age of 73 you can ask to continue having  regular screening mammograms. You are also likely to have a mammogram if you have breast cancer symptoms, such as a lump, but this happens outside the screening service.

How you have a mammogram

A radiographer helps you to position one breast at a time between 2 flat plates on the X-ray machine. The plates press your breast firmly between them for a few moments to take the X-ray. You have 2 X-rays of each breast. The compression of the breast helps to give a clear picture. Having a mammogram can be uncomfortable. Some people find it painful. But the discomfort only lasts for the short time that your breast is compressed.

After the mammogram

Two specialists look at your mammogram to see if there are any signs of cancer. If there is any doubt at all about your mammogram, you will be asked to go back for more tests. Some cancers don't show up clearly on a mammogram. So, if you find any suspicious lump in your breast, always tell your doctor, even if you recently had a mammogram.


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What a mammogram is

A mammogram is an X-ray of the breast.

The NHS breast screening programme uses mammograms to screen for breast cancer in women in the UK from the age of 50 to 70. Women over 70 can request screening every 3 years by contacting their local breast screening unit. In England, the programme is currently being expanded and will offer mammograms to women between the ages of 47 and 73.

The current evidence suggests that breast screening reduces the number of deaths from breast cancer by about 1,300 a year in the UK.


Having a mammogram

A radiographer helps you to position one breast at a time between two small flat plates on the X-ray machine. The plates then press your breast firmly between them for a few moments, to take the X-ray. The compression of the breast helps to give a clear picture. 

You have 2 X-rays of each breast – one from above and one from the side.

View a transcript for the video about having a mammogram.


How a mammogram feels

Some women worry about whether a mammogram will hurt. For most women it is just a bit uncomfortable. Some women do feel some pain, but it is usually only for a few moments while you are having the X-rays taken. Some women may experience discomfort or soreness for a few days after having the mammogram.

A Cochrane review reported that having good information before the test and having control over your breast compression during your mammogram reduces pain. Taking aspirin or paracetamol before the procedure didn't help. If you would like to, you can read this review on pain in mammography in the Cochrane Library. It is written for researchers and specialists and so uses complex language.


After the mammogram

Two people called film readers or image readers look at your mammogram to see if there are any signs of cancer. The film readers are radiologists or radiographers

You should get your results within 14 days. The radiographer should tell you when to expect yours. If the X-ray is not clear enough or shows any abnormal areas, the clinic staff will call you back for more tests. You may need to have the X-rays taken again.


If you are called back

Around 4 out of 100 women (4%) are called back as part of the NHS breast screening programme. But only around 1 in 5 of these women will turn out to have cancer. That's about 8 out of every 1,000 women having breast screening.

So out of every 5 women called back, 4 will be fine. These women will have had some unnecessary anxiety. But doctors and researchers feel that the anxiety for these women is balanced by the screening programme picking up many breast cancers very early on in their development. Very early breast cancers are usually easier to treat, may need less treatment, and are more likely to be cured.

If you are called back because your mammogram showed an abnormal area, you may have a magnified mammogram. This can show up particular areas of the breasts more clearly. They show the borders of any lump or thickened area and can also show up areas of calcium (calcification).


What a mammogram can show

Well developed breast cancers nearly always show up clearly on mammograms.

Image of a mammogram

But no screening test is perfect and unfortunately there will always be some cancers that are missed or do not show up.

With early stage breast cancer, there may be no lump, but your mammogram may show small areas of calcium in particular patterns within the breast tissue. These areas of calcium are called calcification. But calcification can also sometimes occur due to non cancerous changes in the breast. The skill and experience of the technicians and doctors helps them to read the different patterns and decide which might be due to cancer and so need further tests.

Some cancers do not show these clear signs on the mammogram. So, if you find any suspicious lump in your breast, always tell your doctor, even if you recently had a mammogram.


Very early non invasive cancers - DCIS

Your screening mammogram may show DCIS. This stands for ductal carcinoma in situ. It means that there are changes in the cells lining the breast ducts. The breast cancer cells are only inside the ducts of the breast. The ducts are the tubes that carry milk within the breast. In some women DCIS may spread into the surrounding breast tissue after some years, to become an invasive ductal breast cancer.

Diagram showing ductal cancer in situ (DCIS)

There is very little risk of low grade or intermediate grade DCIS coming back once it has been removed with surgery. But if you have high grade DCIS you may need further treatment. You can read about treatments on our page about DCIS.


Possible risks of breast screening

As with all X-rays, having a mammogram exposes you to some radiation, but only a small amount. For every 10,000 women who have regular 3 yearly screening between the ages of 47 and 73, experts estimate that there will be between 3 and 6 extra breast cancers caused by radiation.

Breast cancers found by screening are generally at an earlier stage, when they are more likely to be curable. So, doctors and researchers generally think the benefits of finding breast cancer early outweigh the risk of radiation from screening mammograms.


Breast screening, over diagnosis and over treatment

Screening can also find some very early, slow growing breast cancers that would never cause any problems in a woman's lifetime. It may also pick up some cases of DCIS that wouldn’t ever develop into cancer. But doctors can't tell which early breast cancers or cases of DCIS would never cause a problem. So the safest option at the moment is to treat them all. This means that some women have breast cancer treatment that they wouldn’t have ever needed if they hadn’t been screened. Doctors call this overdiagnosis or overtreatment.

A panel of experts reviewed the evidence on overdiagnosis in breast screening in 2012. They estimate that about 4,000 women each year have treatment for a breast cancer that may never have actually caused them any harm. This is out of about 15,500 breast cancers diagnosed through screening annually. We have more detailed information about the findings of the breast screening review.

We will continue research into finding out more about how to identify women with DCIS that won’t develop into cancer. We are learning more about the different grades of DCIS and that should help in the future. You can find out about trials for DCIS on our clinical trials database. Type 'DCIS' into the free text search box and tick the boxes for closed trials and trial results.


Anxiety about screening

The screening programme can cause unnecessary anxiety and distress for the 4 out of 5 women called back for more tests who turn out to be fine. This needs to be balanced against two things. The programme diagnoses breast cancer early for many women  saving them and their families much more distress. But it also overdiagnoses some women who have a breast cancer that would not go on to cause them any problems.

This is a decision that we all need to make for ourselves. Many women find having regular breast screening very reassuring. They understand that it is very likely to pick up cancers at an early stage when treatments work best.


More about UK breast screening

You can find detailed information about the UK breast screening programme on the NHS breast screening programme (NHSBSP) website. They have various information resources available in different formats that answer questions about breast screening. There is a selection of audio and video resources as well as information and instruction leaflets.

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Updated: 30 July 2014