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A mammogram is a low-dose X-ray used to check breasts for cancer. It is particularly helpful in women who have passed their menopause.

A mammogram is a low-dose X-ray used to check breasts for cancer. It is particularly helpful in women who have passed their menopause. In the UK, women aged 50 to 70 years are invited every three years for a mammogram as part of the breast screening service. Mammograms are also used in breast clinics if you have a breast lump which needs checking.

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What is a mammogram?

A mammogram is a low-dose X-ray of the breasts. X-rays are a type of high-energy radiation. An X-ray machine can produce short bursts of X-rays. The rays pass easily through fluids and soft tissues of the body. However, dense tissue (usually bone in most X-rays) will block some of the X-rays. Density means how much of something there is in a certain amount of space. The more dense the tissue, the less X-rays pass through. For mammograms a lower dose of radiation is used. The picture that results used to be developed on to X-ray film. However, much like normal photographs, this has largely been replaced by digital systems. The X-ray is converted into a digital image of the breast, which is stored on computer. This creates better pictures with a lower radiation dose. In a mammogram, the dense tissue of breast lumps may show up in the picture. Lumps which are cancerous have a particular appearance.

Mammograms can pick up possible breast cancers before they can be felt as a lump.

What is a mammogram used for?

A mammogram is used to detect breast cancer. Because a mammogram can pick up a cancer before a lump can even be felt, it is used as the test in the breast screening programme. In the UK, women between the ages of 50 and 70 years are invited to have a screening mammogram every three years. Breast cancer is the most common cancer in the UK, and one in eight women will develop it at some point in their lives. The idea of the screening programme is to use the early detection power of mammograms to pick up these cancers very early. This means the cancers can be treated at an earlier stage, so that the outcome should be better. It is estimated that for every 10,000 women starting the screening programme, 43 deaths will be prevented.

A mammogram is also used as a test when you have a breast lump, or other changes in your breast. When you have a breast lump, you will normally be referred to a specialist breast clinic for further tests. One of these tests may be a mammogram. In general, mammograms are more helpful in older women who have had their menopause. This is because of the way the breast tissue changes after menopause. So, if you have a lump being checked and you are younger than 50 years old, you may have an ultrasound scan instead. Some women will have both an ultrasound and a mammogram. Other tests, such as a biopsy may be used too. Put together with examination of your breasts by the specialist, these tests will determine if you have breast cancer, or if you have non-cancerous breast changes.

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What will happen when I have a mammogram?

Mammograms are carried out in hospital departments, and also in mobile screening vans. The mobile vans are often set up in local car parks or supermarket car parks to make it easier for women to get to them. They have large NHS signs on them to make it clear what they are.

You will be asked to take off your top and bra. It will be easier for you not to wear a dress - if you wear trousers or a skirt you can leave the clothes on the lower part of your body on.

The technician (usually a lady) is called a mammographer or radiographer. She will position your breasts (one at a time) on an X-ray plate. She will need to move your breasts to get the position right for the X-ray. She will explain how you should stand and ask you to turn your head in a certain way, and place your arm in a certain way. This enables the best picture. The other plate then moves so that your breast is squashed between the two plates. Two pictures will be taken, one in each of two positions. One view is an up-to-down view; the other is an angled view across the breast. This allows a comprehensive picture of the breast tissue. You will be asked to stay completely still while the picture is being taken.

It can be uncomfortable having your breasts squashed in this way, and some women find it painful. However, the picture is taken very quickly and any discomfort should go away as soon as the pressure is off your breasts. Occasionally your breasts can feel a little tender afterwards.

Afterwards you put your clothes back on and go home. For screening mammograms, the result will be sent to you in the post within three weeks. If you are having the mammogram in the breast clinic the result is usually available within a day or two.

The whole appointment usually takes less than half an hour. Each individual mammogram picture takes a few seconds only.

You will normally be asked to let the breast unit know if you have a physical disability, as many of the vans do not have disabled access. An appointment elsewhere may be arranged. You should also let the unit know if you are pregnant or breast-feeding, and if you have breast implants.

Are there any risks to having a mammogram?

A mammogram is generally a very safe test. Possible risks include:

  • The worry factor. It can be an anxious time waiting for test results, and of course it is even more worrying if the test is positive. Most women who are called back after a mammogram do not have breast cancer. So these women have been put through unnecessary worry.

  • When having a mammogram for screening, there is the risk of 'over-diagnosis'. This means there is a possibility that a cancer will be picked up that never would have spread and caused harm. In this case you would be having treatment which was not really necessary. It is estimated that for each death prevented by breast screening, three women have unnecessary treatment. They have treatment for a cancer which would not have caused them any harm.

  • Occasionally the mammogram may be falsely reassuring - it may miss a cancer. This is unusual. It is estimated this happens in one in every 2,500 tests.

  • There is a tiny chance that the X-rays themselves can cause cancer. It is estimated that for every 100,000 women who have a mammogram, between 1 and 10 develop cancer due to the radiation involved.

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What happens if the mammogram shows a problem?

What does breast cancer look like on a mammogram?

If a mammogram is abnormal, further tests will be needed. It is important to bear in mind that most women who are asked to come back after a mammogram do not have breast cancer. It may be that there is a technical problem with the picture and it needs repeating. Or it may mean that there is a non-cancerous lump which has been picked up.

Usually if the mammogram finds a problem on screening, you will be sent an appointment with a specialist breast clinic. The specialist will examine your breasts and will look at the mammogram and decide which tests are needed. You may need an ultrasound scan.

They may decide to take a sample of the part of the breast the mammogram has shown to be abnormal. This can be done by drawing a sample out with a very thin long needle. Or a small sample may be cut out (a biopsy). The breast tissue is then examined under a microscope to see if it contains any cancer.

For every 100 women called back after a routine screening mammogram, about 81 do NOT have breast cancer. If breast cancer is picked up by further tests (either in the screening programme or through investigations for breast changes in the breast clinic) then treatment for breast cancer will begin as soon as possible.

Should I have a mammogram?

If you have been referred by your GP to the specialist breast clinic for a breast lump or other breast change, and the specialist advises a mammogram, this is an easy decision. The mammogram will help to identify whether your breast changes are due to cancer. If they are, your cancer will be treated and hopefully this will be successful.

However, it can be a more difficult decision to decide whether to have a mammogram when you receive an invitation from the breast screening service. On balance the evidence currently suggests that breast screening does save lives. It picks up breast cancers early, which can be treated, preventing death from breast cancer. However, the evidence does also suggest that for each life saved, other women have unnecessary treatment. It is each individual woman's decision. You can only weigh up the benefits against the possible risks (listed above) and then choose to have the screening or not.

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The information on this page is written and peer reviewed by qualified clinicians.

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