Welcome to the genetics section of our website.
Some cancers do run in families. People sometimes think that several cases of cancer in their family might be connected, and that they have inherited an increased risk of developing cancer. However, only a minority of cancers (5–10%, or less than 10 out of 100 cases) are clearly linked to an inherited gene change. Unfortunately, most cancers happen for reasons we don’t fully understand and it may well turn out that more cancers have a genetic origin.
Genes are the biological information passed on (inherited) from your parents. They affect the way your body grows, works, and looks. Every single cell of your body is a tiny building block and contains all the information you inherited. The information is contained in 46 chromosomes (23 pairs) within the nucleus of each cell. Chromosomes are like containers or filing cabinets filled with all the genetic information your body needs to work properly. Chromosomes can actually be seen through a strong microscope. It is estimated that each human cell contains around 30,000 genes.
It seems that cancer, even if there is a strong family history, is almost always the outcome of an interaction between genes and the environment.
A genetic or DNA test looks at the order in which the chemical “letters” of your genetic code are found within a gene. For example BRCA1, the first gene identified as playing a role in hereditary breast cancer, consists of around 100,000 “letters”.
Each cell carries out a specific function for the body and it uses the information contained in its DNA to know what to do. If there is a mistake contained in any of the ‘files’ stored in your body cells, it can make things go wrong with the cell. A cell could die or could grow into tissue that is not quite right (like a cyst) or it could grow and multiply out of control and develop into a cancer.
A genetic test tries to find these mistakes or genetic changes (mutations). A genetic mutation is not in itself a cancer, but it might mean that you are more likely to develop cancerous cells than other people in the population.
Researchers are working hard to understand more about how genes work inside the body and why things sometimes go wrong. Recently, cancer research has focused on understanding how a normal cell, through a series of genetic changes, turns into a cancerous cell. A number of genes have been identified that play a part in the development of some cancers. If a person is born with a gene change (mutation) that makes them more likely to develop cancer, we say that they have inherited a cancer gene. This mutation may then also be passed on to their children.
There are two types of genetic changes or mutations:
- those that are passed down from generation to generation
- those that happen during the lifetime of a person and are not passed on to the next generation
The most common cancers that may, in some cases, be due to an inherited mutation are breast, ovarian, bowel and womb (endometrial) cancer. Genetic tests can identify some of the genes responsible for these cancers. In some cases, other cancers such as prostate, pancreatic and testicular cancer may be caused by an inherited mutation. However, although genes thought to be linked with these cancers have been identified, genetic tests for these cancers have not yet been developed.
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.
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.
For a list of all genetic centres in the NHS – click here.
The increase in risk varies according to the particular genetic mutation and the type of cancer it relates to. For example, 8 in 10 (80%) of women who have a mutation in one of the known breast cancer genes, BRCA1, and a strong family history of the disease, will develop breast cancer. This is a much higher risk than women in the general population have. Only one in ten (10%) of women who don’t have a strong family history will develop breast cancer.
If you are found to have a cancer gene mutation, other members of your family might have inherited the same genetic change that you have. Each of your children will have a 1 in 2 chance (50%) of inheriting the change from you.
Screening becomes very important for some people who know that they are at increased risk. Bowel screening can pick up pre-cancerous cell changes, but other types of cancer screening only pick up cancers at an earlier stage than they might otherwise have been detected. Cancer screening often does not in itself prevent cancer. But it is important to remember that cancers which are detected earlier can be treated more effectively.
Many people say that having gone through genetic counselling and testing, and having regular screening, means that they are doing everything they can to increase their and their children’s chances of good health. For that reason some people also start keeping a simple record of their family’s health and major illnesses. They want to have the information available for their children or other relatives if they ever need it.
Cancers Linked To Genetics
1. Breast cancer
Some risk factors have been found to play a role in the development of breast cancer generally – not only for people who have a strong family history of the disease:
- An early first period (menarche) and late menopause seem to slightly increase a woman’s breast cancer risk.
- The contraceptive pill and HRT may both slightly increase a woman’s risk of breast cancer particularly if taken for more than five years. However, women’s individual situations vary and it is important to talk to your doctor about your own particular risk.
- Other risk factors are being very overweight, particularly after the menopause, and drinking large amounts of alcohol.
The following factors seem to lower women’s breast cancer risk:
- physical exercise
- a diet high in vegetable and fruit content
- having children early in life and breastfeeding them. However, this factor has been questioned for women who have (carry) a BRCA1 or 2 mutation
2. Ovarian cancer
All of the above risk factors also apply to ovarian cancer, except for the contraceptive pill – the pill seems to reduce ovarian cancer risk. If you have a significantly increased breast and ovarian cancer risk in your family (for example, because a BRCA1 or 2 mutation has been found in your family), this can make deciding whether to take the pill difficult. The pill might reduce your ovarian cancer risk but increase your breast cancer risk.
3. Bowel cancer
Here are some risk factors for bowel cancer:
- a history of polyps in the bowel or other chronic bowel problems
- a diet containing a lot of fat and meat and not enough fruit and vegetables
- alcohol and smoking.
The following factors can lower your bowel cancer risk:
- a diet high in vegetable and fruit content and low in fat and salt
- regular, moderate physical exercise.
Not all of the factors listed here are within a person’s control. It is also not clear how all these different factors might interact. There is also no good evidence about how much these factors affect the small group of people who have a strong family history of cancer. However, some people say that if they avoid some of the above risk factors it makes them feel they are doing whatever they can to control their risk of cancer. If you are thinking about ways of reducing your own cancer risk, it is worth discussing your ideas with your specialist so that you can take into account your personal circumstances.
It is clear that giving up smoking, eating a balanced diet, exercising moderately and maintaining a healthy weight is good for you regardless of your cancer risk and can make you feel better in many ways.
A rare cancer of the eye called retinoblastoma, which occurs in childhood, can be hereditary.
Scientists and doctors also believe that there is a genetic cause for testicular, pancreatic, prostate, stomach and kidney cancer in a small number of people.
Currently there is no effective screening available for most of these cancers. If you are worried about a lot of cases of these (or other) cancers in your family, you should talk to your GP. If there is the possibility of a genetic factor playing a role in your family, you might be able to take part in a research study. You will also be told what symptoms to look out for to identify any possible cancer as early as possible.