Genes and cancer
Cancers start when cells become abnormal following changes to genes inside the cell. These changes are called gene mutations or faulty genes.
Most mutations happen during a person’s lifetime but some can be inherited. People with a strong family history of some cancers may need genetic testing to see if they have an inherited mutation.
Genes are the codes inside all the cells in our body. They control how each cell works. A change to a gene is called a gene mutation, or an abnormal or faulty gene.
Not all mutations cause problems, but some affect the way cells behave and increase the chance of cancer developing.
Mutations can be acquired or inherited:
- Acquired mutations happen when cells divide during a person’s lifetime. Most of them have no obvious cause (spontaneous mutations), but some are caused by repeated cell damage, e.g. from radiation, chemicals or getting older.
- Inherited mutations happen when faulty genes are passed on from a parent to some or all of their children. Only 5 to 10% of cancers are linked to inherited mutations.
Who needs genetic testing?
Only a few types of cancer have been linked to inherited mutations. These include some breast, ovarian, prostate, bowel, kidney, pancreas, skin, thyroid, endometrial and eye cancers.
Genetic testing looks for these mutations. If there is a history of cancer in your family, talk to your GP or specialist. They may refer you for genetic counselling and testing.
Not everyone with a family history of cancer has a faulty gene.
What is genetic counselling?
Before genetic testing, most people have an appointment with a health professional called a genetic counsellor.
The genetic counsellor will:
- talk to you about your family history
- tell you whether genetic testing is suitable for you
- explain some of the positives and negatives of testing.
What does genetic testing involve?
Genetic testing involves having a blood test to look for faulty genes (mutations) which can increase the risk of developing cancer.
There are two steps involved:
- A person in the family who has cancer, or had it in the past, gives blood.
- This is tested to see if it has any faulty genes.
- If a faulty gene is found, other family members are tested for the same gene.
- Family members who have the abnormal gene can have an increased risk of getting the same type of cancer.
People with a faulty gene need to understand how this affects their risk of getting cancer. They may need more regular cancer screening than people without the gene.
Tests for bowel cancer genes
There are some inherited gene mutations that can increase the risk of developing bowel cancer.
These gene mutations can cause syndromes which run in families, for example Lynch Syndrome.
If you have a close relative who was diagnosed with bowel cancer before the age of 50, or several relatives with bowel cancer, or relatives with known genetic mutations, you need to talk to your GP. Your GP can refer you to a family cancer centre or genetics service.