In most cases, people who inherit a known cancer gene will not definitely get cancer. Inheriting a cancer gene usually means that a person has a significantly increased risk of developing cancer compared to other people in the population. So you don't inherit cancer from your family, but you might inherit an increased risk of developing cancer. This type of increased risk is sometimes also called a predisposition or susceptibility.

It is important to remember that everyone has a certain risk of developing cancer in their lives, whether they have people in their family with cancer or not. This risk increases with age, which means that old people are far more likely to develop cancer than young people. It is relatively rare for young people to get cancer. This is true even if they have one close relative with cancer. Close relatives are parents, children, brothers, sisters, aunts, uncles and grandparents.

Cancer is a common disease. Almost everyone has a close relative with cancer. Your risk of developing the same type of cancer as your relatives will normally be significantly increased only if you have at least two close blood relatives with the same cancer on the same side of your family (for the very few exceptions to this rule, see bowel cancer or breast & ovarian cancer risks).

As not everyone who inherits a cancer susceptibility gene actually gets cancer, it can sometimes look as if cancer skips a generation in families where many members have cancer. But on a genetic level, you either inherit the gene from one of your parents or you don't. There is a 50/50 chance. If you don't inherit the gene, you can't pass it on to your children. So the genetic mutation cannot skip a generation. However, not everyone with the mutation will necessarily develop cancer, so it can seem that the cancer skipped one generation.

Also, the gene mutations for women's cancers such as ovarian or breast cancer can be passed on through the father's side of the family. Men who have the genetic mutation responsible for breast and ovarian cancer don't normally develop cancer themselves. They can develop breast cancer, but this is extremely rare in men. The genetic mutation can also increase a man's risk of getting prostate or pancreatic cancer. However, in most cases men don't actually develop a cancer related to the genetic mutation they inherited. But they still have a 50/50 chance of passing the genetic mutation on to their children. So, again, it can seem as though the genetic mutation has skipped a generation, if a daughter inherits the breast cancer susceptibility gene from her father.

Mostly we don't know what causes any particular cancer. This can be frustrating, but unfortunately the causes of most cancers can't easily be explained. An obvious exception is lung cancer, which we know is mostly caused by smoking. Cancers that are not caused by an inherited genetic change are called spontaneous or sporadic.

Some situations make it more likely that a certain cancer is caused by an inherited gene change rather than being sporadic. A cancer is more likely to be inherited if:

• there are two or more close blood relatives on the same side of the family affected by the same type of cancer
• a close relative had more than one primary tumour. This means that a person has cancer twice, but the second cancer is not due to the first cancer spreading to another part of the body: it is in fact a new cancer (for example, breast and then womb cancer)
• members of a family get cancer at a younger than normal age (under 60 years)
• certain cancers happen together in a family. There are two main patterns where cancers occur together.

Firstly, there is breast and ovarian cancer, which sometimes run together in a family. Secondly, there is bowel and womb (endometrial) cancer, which sometimes happen together with other cancers such as stomach, kidney, ovarian or pancreatic cancer.

These are also the criteria that your GP, genetic counsellor or consultant will use to assess the possibility of you having inherited a cancer gene. However, these factors only give an estimate of whether or not a family might have an increased risk of developing cancer, because every family is different. Very small families will obviously not have a high number of members with cancer. Similarly, families with more men than women might not show clear patterns of breast and ovarian cancer. In cases of adoption or marriages within the family, the criteria also need to be used flexibly.

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

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 might 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. Your GP will ask you questions about your family history. If your GP thinks there is a chance your family has an inherited increased risk of getting cancer (genetic susceptibility), 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 might also be advised to see a breast care specialist, a gynaecologist or a gastroenterologist, depending on the type of cancer concerned. You might be seen by a specialist nurse, counsellor or doctor.

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 at www.bshg.org.uk/genetic_centres/uk_genetic_centres.htm

After your GP's referral, you will probably have to wait for a few weeks or months before you are seen by a specialist. Waiting times vary and you might want to ask your GP how long people have to wait in your area. If you are very worried about your risk of developing cancer, you might feel tense and anxious about waiting. It is important to remember that even if you do have an increased risk, you are 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 centre or family cancer clinic will look at your referral from the GP and your family history information. They may decide that you are 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 might then turn out, for example, that what you thought was an ovarian cancer actually was a cervical cancer. This might mean that there is no clear pattern of inherited cancers in your family.

In cases like this, the familial cancer or genetics clinic might decide that you do not 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 at all from your GP, or the regional genetics centre, about your referral, it is 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 that 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, you should feel free to call them and speak to a genetic specialist over the phone.