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.
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.
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.
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.
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.
Genetic background may contribute to prostate cancer risk, as suggested by associations with race, family, and specific gene variants. Men who have a first-degree relative (father or brother) with prostate cancer have twice the risk of developing prostate cancer, and those with two first-degree relatives affected have a fivefold greater risk compared with men with no family history.
No single gene is responsible for prostate cancer; many different genes have been implicated.
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.
Prostate cancer screening is an attempt to find unsuspected cancers. Initial screens may lead to more invasive follow-up tests such as a biopsy. Options include the digital rectal exam (DRE) and the prostate-specific antigen (PSA) blood test. Such screening is controversial and, in some people, may lead to unnecessary disruption and possibly harmful consequences.