Understanding the genetics of breast cancer
Breast cancer is a type of cancer where cells in your breast grow uncontrollably, forming a tumour. Both lifestyle and genetics can influence your risk. Genes determine traits like eye and hair colour. They can also affect your risk of developing diseases, including breast cancer. Here I talk about how genetic changes and family history impact breast cancer risk, and how genetic testing can help you understand your personal risk.
What causes breast cancer?
We don’t know for sure why some people get breast cancer. But breast cancer causes are likely to be a combination of genetic, hormonal and lifestyle factors.
You’re more likely to develop breast cancer if you:
- are over 50
- have a biological parent or sister who’s had breast cancer
- carry certain genes changes, such as BRCA1 and BRCA2
- started your periods early or the menopause late
- have never had children or didn't have children until after age 30
- take a contraceptive pill that contains oestrogen
- take hormone replacement therapy (HRT), depending on the type of HRT and how long you take it for
- are overweight once you've passed the menopause
- drink alcohol – the more you drink, the greater your risk
In around half of breast cancer cases, there is no risk factor other than age and being female.
What is considered a strong family history of breast cancer?
Your risk of breast cancer can be increased if you have a first degree relative (a parent or sibling) with breast cancer. If you have a second degree relative (grandparent or aunt) with breast cancer, it can also increase your risk. Breast cancer where there is a strong family history is called familial breast cancer or inherited breast cancer. Most women with breast cancer don’t have a family history of the disease.
Is breast cancer genetic?
Up to 10 percent of breast cancer cases will be caused by genetics. This is when you have a certain gene mutation that will increase your risk of breast cancer.
The most common genes known to increase breast cancer risk are BRCA1 and BRCA2. These genes normally help repair DNA. Having a mutation in these genes can lead to developing breast cancer. When you have the mutated gene, this is called a variant. But having a gene variant doesn’t mean you will definitely develop breast cancer. And it’s possible to have breast cancer without your genes being involved.
BRCA1 and BRCA2 are referred to as high penetrance genes for breast cancer. There are many other gene variants that are involved in breast cancer. So you might have a different gene mutation that is neither BRCA1 or BRCA2.
Speaker 1 Dr Timothy Woodman: When people talk about genes and genetics they maybe mean different things so there's the genetics that you're born with the genes that you've got and any mutations or changes in those genes and then there are genetic changes that do run in families.
Now people may say I'm at risk there's a big history of cancer in my family but as I said you one in two of us may get cancer we're all going to know a family member who's had cancer if you have a large family you're going to think I'm at high risk there's a lot of people in my family with cancer but if you look at things like cancers at an early age in your family that's potentially a risk factor for you.
People who have a history of linked cancers so women who have had breast cancer and ovarian cancer together that's a significant risk factor.
There are some different ethnic groups where there are different risk factors.
People who have had more than one cancer in their lifetime that suggests they may have a genetic problem which could be inherited.
Again if you're worried talk to your doctor.
There are tests that can be done and if you are at risk two things: the fact that you've got a risk factor doesn't mean you're going to get cancer but the fact you haven't got any risk factors doesn't mean you're not going to get cancer so you still have to follow all the advice on healthy eating and not smoking et cetera.
Speaker 2 Dr Zoe Willams: So when it comes to those sort of specific genes, and I think the most common one people have heard of is the BRCA gene when it comes to breast cancer.
What proportion of cancers are linked to specific gene mutations.
Speaker 2: In terms of inherited genes probably not more than about 10 per cent of all cancers.
Pretty well all cancers you could probably trace back to a genetic fault somewhere but it's something that has appeared entirely at random that isn't inherited but 10% is significant and when if you're one of those at risk groups it may mean that your risk could be a lot higher than 10% of getting cancer Speaker 2: It's interesting isn't it because we talk about how genes are inherited from our parents but actually those lifestyle behaviours that you've spoken about are often inherited from our parents as well you know we're more likely to have similar behaviours to what our parents and what our family do.
And then also the environmental things that you know where we live you know if we're exposed to certain chemicals pollution they kind of run in families as well so I guess when you're thinking about your family history it's quite complex isn't it.
Speaker 1: Oh it's very, there are so many different factors in play as you said there Zoe and there's only so much that you can alter.
So it's all about being aware and any worries at all get advice You can get advice from your GP, you can get it from the NHS website, Bupa website, virtual GP consultations with Bupa, there are so many ways now really.
Don't die of ignorance as they once said about another disease.
What should I do if I have a family history of breast cancer?
If you think breast cancer might run in your family, see if your GP can refer you to a genetic specialist. They can talk through your family history with you. If you have a strong family history of breast cancer, you may be able to have a genetic test on the NHS. Genetic testing is also available privately.
Genetic or genomic testing looks at your DNA to identify any gene variants that may increase your risk of certain diseases. This is called predictive testing. Remember, if you have a gene variant for breast cancer, it doesn’t mean you will definitely develop breast cancer.
If you’re having a genetic test, it’s also recommended you see a genetic counsellor. They can help you to understand what your results from predictive testing mean for you and your family.
What happens if you test positive for BRCA?
If your test shows you have BRCA1, BRCA2, or other mutations, you have options to monitor and lower your risk. This includes screening and surgery.
The NHS breast screening programme invites women aged 50 to 70 to have screening every three years. But if you’re at a high risk because of a breast cancer gene mutation, you can have screening at a younger age. You can also have screening every year instead of every three years. Breast screening can help detect breast cancer earlier, when treatment will be more effective.
You can also have breast surgery to reduce your risk. This surgery, known as a mastectomy, removes breast tissue to greatly lower your risk of breast cancer.
How can I prevent breast cancer?
Not all risk factors for breast cancer can be controlled, such as your age and genetics. You might not always know your family history of the disease either. But living a healthy lifestyle is an important step you can take.
You may be able to reduce your risk of breast cancer by:
- maintaining a healthy weight
- being active
- stopping smoking if you need to
- only drinking alcohol in moderation
Our breast cancer screening service can help to identify early signs of breast cancer before any noticeable symptoms appear. You can discuss any worries you have with a GP, and the appointment includes a physical breast check and a mammagram.
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