Mammograms in breast screening

A mammogram is an X-ray of the breasts. The NHS breast screening programme uses mammograms to screen for breast cancer in women in the UK from the age of 50. The breast screening programme is currently being expanded and will offer mammograms to women between the ages of 47 and 73 by 2012. Women over 73 can request screening every 3 years by contacting their local breast screening unit. 

In 2009, experts looked back at the results of all the breast screening trials carried out from the 1960s to the 1990s.  All the results together suggested that breast screening can reduce the number of deaths from breast cancer by about 15% in women who are regularly screened. Put another way, this means one life saved for every 2,000 women screened for 10 years. This adds up to about 500 lives saved in the UK each year.  But there is still a lot of debate about this.  Some scientists think the benefits are much greater, at around 1,400 lives saved per year in the UK. But another European study looking at breast cancer deaths since the 1980s suggests that breast screening may not save as many lives as we thought.

A radiographer helps you to position one breast at a time between two small flat plates on the x-ray machine. Your breast is then pressed firmly between the plates for a few moments, to take the x-ray. 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.

Women in the UK have 2 X-rays taken – one from above and one from the side. This gives a higher chance of picking up changes in the breast tissue that could be due to a cancer. Researchers have shown that taking a 2 view mammogram each time increases the breast screening programme's cancer detection rate by 25% to 45%. So, more women have their cancers found early when they are easier to treat.

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 only for a few moments while you are having the X-rays taken. A Cochrane review carried out in 2008 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.

Two radiologists look at your mammogram to see if there are any signs of cancer. 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 just need to have the X-rays taken again.

About 1 in 20 women (5%) are called back as part of the NHS breast screening programme. But only around 1 in 8 of these women will turn out to have cancer. That's only about 7 out of every 1,000 women having breast screening.

So out of every 8 women called back, 7 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 extra mammograms called coned down magnification views. These can show an area of the breasts more clearly. They show the borders of any lump or thickened area more clearly and can also show up areas of calcification.

Well developed breast cancers nearly always show up clearly on mammograms. No screening test is perfect, however, 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.

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.

There is very little risk of DCIS coming back once it has been removed with surgery.

As with all X-rays, having a mammogram exposes you to some radiation, but only a small amount. Scientists have worked out that there is less than a 1 in 25,000 risk of the radiation from a mammogram causing breast cancer. About 7 breast cancers are found for every 1,000 women screened as part of the UK breast screening programme. And in these women the cancers are generally at an earlier stage, when it is more likely to be curable. So, doctors and researchers generally think the benefits of finding breast cancer early far outweigh the small risk of radiation from screening mammograms.

Some doctors have been concerned that some women have changes found on mammograms that are not cancer. But they need further tests to show that it is not a cancer. Being asked to go back for more tests can cause worry. Some tests may be uncomfortable, such as a biopsy (having a small tissue sample removed under local anaesthetic).

Screening can also find some very early, slow growing breast cancers that would never cause any problems in a woman's lifetime. Because we can't tell which are the slow growing cancers, some women have breast surgery that may be unnecessary. Some doctors feel that this is a big problem. The UK breast screening programme estimates that about 1 in 8 women who have a cancer found by screening have a lumpectomy instead of mastectomy because their breast cancer is found so early. A lumpectomy is where only the cancer and a margin of breast tissue is removed, rather than the whole breast.

Screening may also pick up some cases of DCIS that wouldn’t ever develop into a cancer. Research by Cancer Research UK estimates that up to 1 in 3 cases of DCIS found by breast screening might not develop into invasive cancer if they weren’t treated. We don't know for sure which ones those are, or how many women are affected. As we can’t tell at the moment which cases of DCIS are going to develop into an invasive cancer, the safest option is to treat them all. So some women with DCIS may have unnecessary treatment.

So some women may have surgery they don’t need, but many more are having potentially life saving treatment. All we can do is 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. The IBIS 2 trial is currently looking into the detection and treatment of DCIS. 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.

Cancer Research UK is working with the National Cancer Director on an independent review of breast screening to look at all the benefits and risks. You can find information about the breast screening review on the News and Resources section of the Cancer Research UK website. The review is also looking at the information given to women about breast screening.

Some people say that the screening programme causes unnecessary anxiety and distress for the 7 out of 8 women called back for more tests who turn out to be fine. But this needs to be balanced against the fact that the programme diagnoses breast cancer early for many women and so saves them and their families much more distress. This is a decision that we all need to make for ourselves. Many women find having regular breast screening very reassuring, knowing that it is very likely to pick up cancers at an early stage when treatments work best.