Disadvantages and risks of breast screening

All x-rays, including mammograms, involve a small amount of radiation. The amount of radiation given during a screening appointment is very small and unlikely to cause any harm. Therefore, the radiation risk associated with having a mammogram every three years is considered to be far outweighed by the benefits of detecting a breast cancer at an early stage, when it is more likely to be curable.

The radiation dose given by breast screening x-rays is continually monitored to make sure that it is as low as possible while still giving a good-quality image. X-ray machines are also carefully checked to make sure that they don’t accidentally expose people to too much radiation.

If you’re concerned about the risk of having a mammogram, talk to the staff at the screening unit. You can find detailed information about the radiation risk of breast screening from the NHS website|. You can also telephone the NHS Response Line on 08701 555 455.

Mammograms can sometimes show an abnormal area in the breast that is later found not to be a cancer when further tests are carried out. This is known as a false-positive result. Waiting to get results of further tests can be a very worrying time, and some women may continue to feel anxious even after they’ve been told they don’t have breast cancer (a negative result).

About 1 in 20 women who have breast screening will have an abnormal result and be asked to go for further tests. The tests may include more mammograms, ultrasound scans or biopsies of the breast tissue, which can cause pain or scarring. Most of the women (around 7 in 8) asked back for further tests won’t have breast cancer.

One or two mammograms in every 100 have to be taken again because:

• The x-ray picture is blurred and cannot be read by the doctor.
• There is some kind of equipment failure, for example the machine that processes the x-ray films breaks down (this is very rare).
• The mammogram misses part of the breast and it needs to be retaken so that the whole breast can be seen.

Although mammography is the most effective and reliable way of detecting breast cancer early, it is not perfect. A breast cancer may not be detected by mammogram because:

• Some cancers are very difficult to see on the x-ray.
• Some cancers, even though they are there, cannot be seen on the x-ray at all.
• The person reading the x-ray may miss the cancer. This will happen occasionally, no matter how experienced the person reading the x-ray is. To reduce the risk of a cancer being missed all mammograms are looked at by two people.

Women having three-yearly breast screening may be diagnosed with breast cancer in the time between their screening appointments, even if they had a normal result after their last mammogram. This is known as an interval cancer.

If an interval cancer is diagnosed, the mammography films taken at the time of diagnosis will be compared to the previous mammograms. Women diagnosed with an interval cancer will always have the results of this review discussed with them. Research shows that the outlook and cure rates for women with interval cancers are better than for women who have never attended screening.

It is possible that a mammogram could find a breast cancer that would never have caused a problem during the woman's lifetime. Unfortunately, it is not possible to tell the difference between cancers that do cause problems and those that will not.

Research suggests that for every 200 women who have breast screening, one will have treatment that may not be needed. About 1 in 8 of all breast cancers detected would not have caused problems. This means that most women who are diagnosed with breast cancer as a result of breast screening do need treatment, because their cancers would have gone on to develop and cause problems without treatment.

It can be difficult to decide whether to have breast screening. The doctors and nurses at the breast clinic can give you more information to help you make an informed decision.

As breast screening can't pick up every cancer, you should see your GP if you have any unexplained changes in your breasts including lumps, pain and discharge from the nipples. You should see your GP even if you are having regular breast screening and have recently had a normal mammogram. 

There are many reasons for changes in breast tissue. Most of them are harmless, but you should always get them checked as there is a small chance that the changes could be the first sign of cancer.