What is a gene? In every cell in the body there is a structure called a nucleus. The nucleus controls the cell. Inside the nucleus are 23 pairs of chromosomes made up of genes. Genes are coded messages that tell cells exactly how to behave. They control how our bodies grow and develop. We have about 25,000 genes. We inherit genes from both parents.
How can genes cause cancer? All cancers develop because something has gone wrong with one or more of the genes in a cell. A change in a gene is called a ‘fault’ or ‘mutation.’ These faults can make a cell stop working properly. It may then become cancerous and divide and grow uncontrollably. Most gene changes happen during our lifetime, but some can be inherited from a parent.
Inherited cancer genes – This occurs when there is a fault in the genes in an egg or sperm cell at the time of conception. These faults in the initial egg or sperm cell are copied into every single cell in the body. The faulty genes can then be passed from generation to generation. This is also called germline mutations.
Parent with a gene fault – A child has 1 in 2 (50%) chance of inheriting faulty genes, resulting in an increased risk of developing cancer. Being born with inherited faulty genes doesn’t mean that a person will definitely get cancer, but that they have a higher risk of developing particular types of cancer than other people. Cancers due to faulty genes are much less common than cancers due to gene changes due to other factors. Genetic specialists estimate that 5-10% of every diagnosed cancer is linked to an inherited gene fault.
Family history of cancer – In families with an inherited faulty gene, there is usually a pattern of specific types of cancer running in the family for example breast or prostate cancer. The strength of family history depends on: who in the family has had cancer, the types of cancer they have had, how old they were at diagnosis, how closely related the relatives with cancer are to each other.
Strong family history – Cancers developed when the family members were young (under 50 years for breast, bowel and womb cancer), multiple close relatives on the same side of the family have had cancer (either your father’s relatives or your mother’s relatives), the relatives have had the same type of cancer, or different cancers caused by the same gene fault, one of your relatives has had a gene fault found by genetic testing can give rise to a strong family history.
If you have concerns over a faulty gene or a strong family history speak to your GP and ensure that you have as much information about your relatives’ cancer diagnoses as possible. If there is concern of increased risk, then you can be referred to a genetics clinic for testing and treatment.
You may be eligible for an NHS genetic test if cancer runs in your family and you are concerned that you may get it too. You can also have private genetic testing.
Tests – Testing for genes that increase the risk of cancer is called predictive genetic testing. The GP will firstly need to work out if you have a strong history of cancer (multiple close family members on the same side of the family who have the same cancer or related cancer types) and will then refer you to a genetic clinic.
Genetic Clinic – Once you are referred to a genetic clinic, you will be asked by the genetic specialist or counsellor about your family history, who will work out the risk of developing cancer and work out whether you need a genetic test. You will be offered a genetic test if you have a strong family history of cancer and the specialist thinks this might be caused by an inherited faulty gene.
Faulty Genes – There are many inherited faulty genes that can increase you chance of developing cancer.
Advantages of genetic testing – if you are found to have a genetic fault, you can reduce your risk of developing cancer by making certain lifestyle changes, having regular screening, take medicine to lower the risk of developing cancer or have the option of risk reducing surgery.
Disadvantages of genetic testing – some genetic test results identify a variation in a gene, but it may not be clear whether it increases your cancer risk or not. You will also have the constant worry about developing cancer if a faulty gene is found. If tested positive, you may need to tell other relatives that they may have inherited the same gene.
Children under 18 years and genetic testing – children cannot usually be tested because they are not old enough to make their own choice about whether to have the test or not. There are exceptions to this, testing for genes that can cause cancer at a young age and for which there is screening that work well.