Cancer risk

Mostly we don’t know exactly what causes any particular cancer but we do know some of the risk factors for cancer. 

A risk factor is something that may increase your chance of developing the illness. Having risk factors for a cancer may mean the chances of you developing that cancer are increased but doesn’t mean you’ll definitely get cancer.

Smoking is a good example of this. If you smoke, it isn’t certain that you’ll get lung cancer - just as if you don’t smoke, it’s not certain that you won’t. But smoking will greatly increase your risk of getting lung cancer. About 9 out of 10 people who develop lung cancer are smokers.

For most people, increasing age is the biggest risk factor for developing cancer. In general, older people (those over 65) are far more likely to develop cancer than younger people (those under 50).

Inherited cancers Back to top

If a cancer occurs more frequently in a family than would be expected in the general population, this may be a sign that some people in the family have inherited a cancer susceptibility gene (see our section on cancer and genes| for more information). It’s thought that about 5–10% of many cancers (between 5 and 10 out of every 100 cases) may be linked to inherited genes.

Scientists have discovered cancer susceptibility genes for some of the more common cancers that sometimes run in families, such as cancers of the breast|, bowel|, ovary| and womb|. There are also other cancers, such as prostate|, pancreatic| and testicular| cancer, which may run in families but specific cancer susceptibility genes for these cancers haven’t yet been identified.

Sometimes there are a number of different types of cancers in a family. Usually these cancers are unrelated and are due to the effects of a combination of risk factors such as age, lifestyle and the environment. But in some cases when cancers such as breast and ovarian cancer| or bowel| and womb| (endometrial) cancer run together in a family, it can be a sign of an inherited susceptibility gene.

There are also some very rare inherited gene mutations that increase a person’s risk of getting several different types of cancer at a young age. In families that have these cancer susceptibility genes several people may be diagnosed with cancer in childhood, adolescence or in their twenties or thirties. We have information about these information about these rare conditions |and our cancer support specialists can also give you information about rare cancers.

Having an inherited cancer susceptibility gene means that a person has a significantly increased risk of developing certain cancers compared to other people in the population. But in most cases, people who inherit a cancer susceptibility gene won’t definitely get cancer. So you don’t inherit cancer from someone in your family, but you might inherit an increased risk of developing a certain type of cancer. This type of increased risk is sometimes also called a predisposition or susceptibility.

In many families with higher than expected numbers of cancers, the cancers are not caused by a strong cancer susceptibility gene. It’s thought that for some of these families their increased risk may be caused by several genes which, in combination with lifestyle and environmental risk factors, affect the risk of getting certain cancers. These genes have a weaker effect on the risk of cancer than cancer susceptibility genes so they are sometimes called ‘low risk’ genes or ‘low penetrance’ genes.

Only a few low penetrance genes have been identified so far. Researchers are trying to find out what these genes are, and how, in combination with lifestyle and environmental factors, they might affect an individual’s cancer risk. 

If there may be a cancer susceptibility gene in your family Back to top

If two or more blood relatives on the same side of your family have developed the same type of cancer at a fairly young age, (or cancers which run together, like breast and ovarian or bowel and womb cancer) you may want to tell your GP.

You should also let your GP know if you have a relative who developed breast, ovarian, bowel or womb cancer when they were very young. If your GP thinks there is a chance that some people in your family have inherited an increased risk of getting cancer, they will refer you to a genetic counsellor or a cancer specialist. This could be in a family cancer clinic or cancer genetics clinic.

You could also try to speak directly to a specialist at your nearest family cancer clinic or genetics centre. However, such specialists usually prefer to see people who have been referred by their GP. You can find a list of all genetic centres in the NHS on The British Society for Human Genetics website|.

If you’re worried that breast and/or ovarian cancer may run in your family there is an online interactive software program (OPERA)| on our website. It can give you personalised information about your breast and ovarian cancer risk. OPERA is based on guidance on familial breast cancer from the National Institute for Health and Clinical Excellence (NICE). This is an independent body that gives guidance to doctors and patients on NHS services in England and Wales.

OPERA isn’t intended to take the place of professional genetic counselling services, so if you are concerned about genetic risk you should still consult your doctor.

Your GP, genetic counsellor or consultant will use a number of criteria in your family history to assess whether there may be an inherited cancer susceptibility gene in your family. A cancer is more likely to be linked to an inherited gene if:

• There are two or more close blood relatives on the same side of the family affected by the same type of cancer. Close relatives are parents, children, brothers, sisters, aunts, uncles and grandparents.
• A close relative had more than one primary cancer. This means that a person has cancer twice, but the second cancer was a new cancer (for example, breast and then ovarian cancer) and was not due to the first cancer spreading to another part of the body.
• Members of a family get cancer at a younger age (under 60).
• Certain cancers have occurred together in the same family. There are two main patterns where cancers occur together (although other very rare patterns of cancers also occur):
  - breast and ovarian cancer
  - bowel and womb (endometrial) cancer, sometimes with other cancers such as stomach, kidney, ovarian or pancreatic cancer.

If you have only one elderly relative with breast, bowel or any other cancer, it’s very unlikely that the cancer is hereditary. If there were an inherited cancer susceptibility gene in your family, it’s very likely that more relatives would have been diagnosed with the same type of cancer.

These factors can only give an estimate of whether or not a family may have an increased risk of developing cancer. Every family is different. Very small families obviously won’t have a high number of members with cancer. Similarly, families with more men than women may not show clear patterns of breast and ovarian cancer. In cases of adoption the criteria also needs to be used flexibly.

Cancer is a common illness. Almost everyone has a close relative with cancer. But, in general, your risk of developing the same type of cancer as your relatives is only significantly increased if you have at least two close blood relatives with the same cancer on the same side of your family. For the few exceptions to this rule, see our information about rare conditions|.

After referral to a genetics clinic Back to top

After your GP's referral, you'll probably have to wait for a few weeks or months before you are seen by a specialist.

It's important to remember that even if you do have an increased risk, you're not in immediate danger of developing cancer within the next few weeks. A few weeks or months wait will not make any difference to your cancer risk or to the advice you will be given.

The genetics clinic or family cancer clinic will look at your GP's referral and your family history information. They may decide that you're not at an increased risk of developing cancer after all. The staff may write to you and ask for your consent to check your relatives' health care records to find the specific type of cancer they had. It may then turn out, for example, that what you thought was an ovarian cancer actually was a cervical cancer. This may mean that there is no clear pattern of inherited cancers in your family.

In cases like this, the family cancer or genetics clinic may decide that you don't need to be seen. The regional genetics centre or your GP should tell you if this decision has been made. However, sometimes this doesn't happen. So if after a few months you haven't heard from your GP, or the regional genetics centre, about your referral, it's worth checking with your GP. If the genetic specialists decide that it isn't necessary for you to see them, their letter to you should include a phone number you can call to discuss the reasons for this decision.

If you have any questions about how they reached their decision, and what this means for your cancer risk, feel free to call them and speak to a genetic specialist over the phone.