GenesWe inherit genes from our parents. Genes determine many body characteristics, including hair and eye colour. We can also inherit conditions and diseases, or a higher risk of them, including breast cancer.
Having a faulty high-risk gene linked to breast cancer is not common, says Professor Gareth Evans, consultant medical geneticist at St Mary’s Hospital in Manchester. “Mutations in the high-risk genes affect one in 500 people or less,” he says.
Genes called BRCA1, BRCA2 and TP53 are linked with breast cancer. Everyone has these genes. If there’s a fault or mutation in one of them, the risk of breast cancer is high.
These faulty genes also increase the risk of ovarian cancer. A blood test can identify whether you have a fault in one of these high-risk genes.
What is the normal risk of breast cancer?
In the UK a woman's lifetime risk of developing breast cancer is 10%. Out of every 100 women, 10 will develop breast cancer by the time they are 80 years old. It can affect anyone. You can get it if you don't have a faulty gene.
If more than one person in a family has breast cancer, this doesn't mean the faulty genes are present. It could be chance, as breast cancer is common.
What is the risk if you have a faulty gene?
If you have a faulty gene, it doesn't mean you'll definitely develop breast cancer, but you are at a higher risk.
Having a fault in one of the breast cancer genes raises the risk of developing breast cancer to between 50% and 85%. Out of every 100 women with a faulty gene, between 50 and 85 of them will develop breast cancer in their lifetime.
Who is tested for faulty genes?
If a woman is diagnosed with breast cancer and has a strong family history of breast and/or ovarian cancer, she will usually be offered a blood test to see whether she has a faulty gene. If the test is positive, this means she has a higher risk of developing cancer in her other breast and of developing ovarian cancer.
Women who don’t have breast cancer can be offered testing if they are at risk of having a faulty gene. This can include relatives of women with a faulty gene, and women with a strong family history of breast cancer where a living family member with breast or ovarian cancer is available for testing.
“Women who have a mother or sister who has tested positive can opt for a simple genetic test to find out whether they’ve got the faulty gene,” says Evans
If you don’t have a relative who has tested positive for a faulty gene, family history needs to be strong to justify testing. "Looking at family history means looking at the combinations of breast and ovarian cancer, and young-onset [younger than 50] breast cancer in the family," says Evans.
"For example, a family history of three women in their 30s or four women in their 40s having cancer would easily qualify someone for genetic testing.”
What if a woman without cancer has a faulty gene?
Because a woman with a faulty gene has a high lifetime risk of breast and ovarian cancer, she has options. Depending on her age and estimated risk, she’ll be offered mammograms or MRI (magnetic resonance imaging) scans or both.
She can still follow general health advice, too. “Women can reduce their risk by not putting on weight, by eating a good diet and by taking regular exercise,” says Evans.
“The problem is that they probably can’t reduce their risk to below 50%. That’s why a high proportion of those women opt for risk-reducing surgery.”
This involves surgical removal of the breasts (mastectomy) and sometimes removal of the ovaries (oophorectomy), to reduce the risk of cancer developing. These are major operations, and the woman and her clinician need to discuss the risks and implications before any decisions are taken.
“If a woman has a double mastectomy [removal of both breasts] her risk of developing breast cancer is reduced by 90 to 95%,” says Evans.
Women who have had risk-reduction surgery will be monitored to check that cancer isn't developing in any leftover breast tissue that can’t be removed, such as on the chest wall.
Where can I go for help if I’m worried about my risk?
If two or three women in your family have had breast cancer and you’re worried about your risk, see your GP.
If your GP thinks you have an increased risk, you can be referred to a local breast clinic. If there is already a positive gene test in the family, they can refer you to the genetic clinic.