Only 5 to 10% of cancers are thought to be linked to inherited genes. But if there are several people who’ve had cancer in your family, you may be concerned about your own risk. If you’ve had cancer yourself, you may worry about your relatives’ risk.
In this blog, we’ll tell you a bit about cancer genetics, and offer you some resources that can help you understand more about your cancer risk.
So, first off, what are genes and how do they relate to cancer?
The organs and tissues of the body are made up of tiny building blocks called cells. Every single cell in our body contains all the biological information we inherit from our parents. This information is stored in our genes in the centre (nucleus) of every cell. Genes affect the way we look and how our bodies grow and work.
The information in our genes is written in a ’code’ made up of four chemicals: adenine, thymine, cytosine and guanine. This is known as DNA.
The genes are arranged together on chromosomes.
Cancer is the result of changes (alterations) in genes that control cell growth and death.
New cells are made and old cells die in our bodies all the time. Genes inside each cell maintain this balance by controlling how the cell behaves. But sometimes, if a gene in a cell is altered, it can cause this process to go wrong. These alterations allow the cell to start growing in an uncontrolled way and develop into a lump (tumour). Usually, several gene mutations must happen in a group of cells before cancer actually develops. This can take many years, which is why cancer is more common in older people.
There are two types of mutation that can happen:
1. The genes have been damaged during the person’s lifetime. For example, lung cells are damaged by smoking or skin cells are damaged by UV light.
2. The person was born with a mutation in a certain gene. This mutation is inherited and passed down from generation to generation. Different gene mutations can cause increase the risk of different types of cancer.
Most cancers are not caused by inherited cancer genes.
And if one or two of your relatives have had cancer, this doesn’t necessarily mean there is a cancer gene in your family.
It's only likely that a cancer gene is present in your family if:
- One of your parents, children or siblings has had two different types of cancer (not one cancer that has spread).
- Two or more closely related people in your family have had the same type of cancer, or types of cancer that are sometimes connected (such as breast and ovarian, or bowel and womb).
- Members of your family have had cancer at an unusually young age (for example, breast cancer under the age of 40).
If you’re worried about a history of cancer in your family, talk to your GP. They may be able to reassure you or refer you to a clinical genetics service or family cancer clinic. You can also call us on 0808 808 00 00, or use some of the resources mentioned below.
People with a strong family history of some types of cancer (bowel or breast cancer) may be offered earlier or more frequent screening than other people.
Some gene changes, that increase the risk of getting breast, ovarian, bowel or some rarer cancers, have been identified. If you have a strong family history of one of these cancers, you may be offered a genetic test. Genetic testing is normally only possible if you have a relative with one of these cancers who is willing to be tested.
We have a range of free information about cancer and genetics. We have five handy leaflets that look at the risk of inheriting cancer in general, and more specifically bowel, prostate, breast and ovarian cancer. They also explain how to reduce your risk. Our booklet on cancer genetics has more detail on cancer genes, inherited cancers, genetic testing and coping with a high risk. We also have a booklet on risk-reducing breast surgery. And all of this information is on our website at macmillan.org.uk/genetics
For anyone worried about breast or ovarian cancer in their family, our online tool OPERA could help. It asks a series of questions about your family history before giving a personalised risk assessment with lots of further information and support. For many people, this tool offers reassurance. For others, it can provide something concrete to discuss with your GP, making sure you get the help you need.
“I was given confidence from my OPERA results to ask for the referral I received.”
Female, 34, from Northamptonshire. Lost her mother to breast cancer at 39 and fears that cancer may run in the family.
If you have any other questions or concerns about cancer genetics, call our cancer support specialists on 0808 808 00 00, Mon–Fri, 9am–8pm. They can give you the information and support you need.
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