Cancer genetics - bowel cancer
Sometimes, people worry about getting bowel cancer because a relative has had it.
Bowel cancer is the third most common cancer in the UK for men and the second most common cancer for women. Every year more than 40,000 people will develop it. So if you just have one elderly relative who had bowel cancer, it’s unlikely that you will have a significantly increased risk.
Most of the time, we don’t know exactly what causes any particular cancer. But we do know some of the risk factors for cancer. Risk factors are things that can make you more likely to develop cancer. They include things such as being older, smoking and being overweight.
Some risk factors are very likely to cause cancer. Others only slightly increase the risk of getting it. Usually, cancer is the result of a combination of several risk factors.
Having a particular risk factor doesn’t mean that you’ll definitely get cancer - just as not having any risk factors doesn’t mean you won’t.
Smoking is a good example of this. If you smoke, it isn’t certain that you will get lung cancer - just as if you don’t smoke, it’s not certain that you won’t. But smoking will greatly increase your risk of getting lung cancer. About 9 out of 10 people who develop lung cancer are smokers.
For most people, increasing age is the biggest risk factor for developing cancer. In general, older people (those over 65) are far more likely to develop cancer than younger people (those under 50).
Cancer is very common. Most of us have relatives who’ve had cancer. People often worry that a history of cancer in their family greatly increases their risk of developing it. But in fact, fewer than 1 in 10 cancers (5–10%) are associated with a strong family history of cancer.
We have more detailed information about the signs and symptoms of bowel cancer, which might be helpful.
How does family history affect my bowel cancer risk?
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Most bowel cancers aren’t caused by inherited cancer genes and most people who get bowel cancer don’t have a family history of it.
In general, the more members of your family who have been diagnosed with bowel cancer (or related cancers such as womb or ovarian cancer), the younger they were when diagnosed, and the more closely related they are, the more likely it is that there’s a family link.
If you have one relative who developed bowel cancer at an older age, this doesn’t significantly increase your risk.
Your risk of developing bowel cancer may be significantly increased if:
one of your first-degree relatives was diagnosed with bowel cancer before the age of 50 - first-degree relatives are your parents, brothers, sisters or children
one of your first-degree relatives, and one of their first-degree relatives, were diagnosed with bowel cancer at any age (for example, your father and his sister)
you have relatives with bowel and womb cancer on the same side of the family
you have relatives with multiple growths (polyps) in the bowel.
If you’re worried about a history of bowel 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.
People with a family history of bowel cancer may be assessed as having low risk, moderate risk or high risk.
This means that your risk of developing bowel cancer is about the same as other people of the same age in the UK.
If you have a low risk, the chance of you developing bowel cancer over your lifetime is estimated to be about 5-9% (between 5 and 9 in 100).
Low risk doesn’t mean no risk, so it’s still important that you take part in the national bowel screening programme when you’re invited to.
This means you have a higher risk of bowel cancer than average. But, you are far more likely not to get bowel cancer than to get it.
If you have a moderate risk, it’s estimated that your lifetime risk of developing bowel cancer is about 10-17% (between 10 and 17 in 100).
This means that your lifetime risk of developing bowel cancer is estimated to be higher than 17% (more than 1 in 6).
Some people have a high risk of developing bowel cancer because they have inherited an altered gene (cancer gene) that greatly increases their risk. The main conditions linked to inherited cancer genes are FAP and Lynch syndrome (also known as Hereditary Non-Polyposis Colorectal Cancer, or HNPCC).
If there is a cancer gene running in a family, usually several relatives on the same side of the family are diagnosed with bowel cancer. In Lynch syndrome, there may also be other cancers in the family that are related to bowel cancer, such as womb or ovarian cancer. People in the family may also be diagnosed with cancer at a particularly young age.
If you're at increased risk
If you’re assessed as having an increased risk of bowel cancer, you’ll usually be offered additional bowel screening - see below. Depending on your estimated risk, you may also be offered other treatments to reduce your risk. There's more information about these on our pages about FAP and Lynch syndrome.
Rarer genetic conditions
A rare genetic condition called MYH associated polyposis (MAP) can also increase the risk of bowel cancer. MAP causes polyps to develop in the bowel. It’s caused by a fault in a tumour suppressor gene called the MYH gene. We have two copies of each gene - one from each parent. A person needs two faulty copies of the MYH gene to be at increased risk of MAP. This makes it far less likely for children to inherit the susceptibility from their parents. Both their parents would need to carry the MYH genetic mutation, and the child would need to inherit the faulty copy from both parents.
Other risk factors for bowel cancer
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Most people who develop bowel cancer don’t have a family history of it. Other factors can affect the risk of developing bowel cancer.
For most people, other factors have a bigger effect on their risk of bowel cancer than family history.
Getting older is the single biggest risk factor for bowel cancer. Most people who get bowel cancer (80%) are over 60.
Inflammatory bowel conditions
Having ulcerative colitis or Crohn’s disease can increase the risk of developing bowel cancer.
If you have an inflammatory bowel condition, a doctor who specialises in bowel diseases (gastroenterologist) will assess your risk and may offer you regular bowel screening with a colonoscopy.
Bowel polyps are non-cancerous growths on the lining of the bowel. If you’ve had certain types of bowel polyps, your risk of bowel cancer is increased and you may be offered screening with a colonoscopy.
A diet high in red or processed meat and low in fruit and vegetables increases your risk of bowel cancer. Processed meats are meats that have had preservatives added or that have been preserved by salting, curing or smoking. They include sausages, ham and burgers.
Smoking tobacco, especially over a number of years, increases the risk of developing bowel cancer.
Being overweight can increase the risk of developing bowel cancer, especially for men.
People who aren’t physically active are more likely to develop bowel cancer.
Bowel cancers that could be prevented by changes
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Over half of bowel cancers in the UK could be prevented by changes in lifestyle.
Here are some things you can do to reduce your risk of bowel cancer.
Eat a healthy diet
Following a healthy diet can reduce your risk of bowel cancer.
Eat plenty of fibre, such as beans, oatmeal, fruit and vegetables. Aim to eat five portions of fruit and vegetables every day.
Avoid processed meat and reduce the amount of red meat, fat and salt you eat.
Keep physically active
Regular physical activity can reduce your risk of bowel cancer. Being physically active doesn’t necessarily mean going to the gym - regular walking, cycling or swimming can be enough.
Try to do at least 2½ hours of moderate-intensity physical activity a week. This could be made up of 30 minutes of activity each day for five days. You could even break it up further into 10 minutes of activity, three times a day.
Moderate-intensity activity is where you’re still able to talk, but your breathing is quicker and deeper. Your body is warming up, your face may have a healthy glow and your heart is beating faster than normal but not racing.
If you’re not used to exercise, your GP can advise you on getting started.
Keep to a healthy weight
The latest figures for the UK estimate that more than half of adults (61%) are overweight.
If you are overweight, getting back to a healthy weight will help reduce your risk of bowel cancer.
Leading an active lifestyle, following a healthy diet and controlling the size of your portions can help you maintain a healthy weight. Your GP can give you more advice on your ideal weight and on losing weight.
Give up smoking
Smoking tobacco increases your risk of developing bowel cancer and many other types of cancer. If you smoke, giving up is the single most important thing you can do for your health.
Help is available if you want to give up smoking. Ask your GP for advice, or contact your national stop smoking service.
Tel 0800 022 4332
(Mon-Fri, 9am-8pm, Sat-Sun, 11am-4pm)
Tel 0800 84 84 84
Stop Smoking Wales (Wales)
Tel 0800 085 2219
Smokers’ Helpline (Northern Ireland)
Tel 0808 812 8008
Limit how much alcohol you drink
Drinking more than four units of alcohol a day can increase your risk of bowel cancer.
The European Code Against Cancer recommends that to reduce cancer risk, men should drink no more than two units of alcohol a day and women no more than one unit.
A unit is half a pint of ordinary strength beer, lager or cider, one small glass (125ml) of wine, or a single measure (25ml) of spirits.
Making the lifestyle changes described here doesn’t mean that you definitely won’t get cancer, but they make it less likely and will improve your health generally.
Screening for bowel cancer
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Screening aims to detect changes in the bowel before cancer develops, or to detect cancer at an early stage when it’s most likely to be cured.
There are bowel screening programmes in all four countries in the UK:
In England and Wales, screening is offered every two years to people aged 60-74.
In Northern Ireland, it’s offered every two years to people aged 60-71.
In Scotland, it’s offered every two years to people aged 50-74.
People older than this can contact their GP if they’d still like to have bowel screening.
These screening programmes involve taking an FOB test (FOBt). The test can detect tiny amounts of blood in your bowel motions, which may be caused by a cancer. You do the test at home and then send it away for checking. People with blood in their bowel motions are asked to have further tests.
Taking part in FOBt bowel cancer screening reduces the risk of dying from bowel cancer.
Bowel scope tests
For this type of screening, a doctor or nurse gently puts a long, flexible tube into your back passage to look for any changes in the bowel.
There are two types of bowel scope:
A flexible sigmoidoscopy looks at part of the large bowel (the rectum and the first part of the colon).
A colonoscopy looks at all of the large bowel (the rectum and the colon).
A bowel scope can detect cancers in the bowel. It can also find and remove polyps, which could otherwise turn into cancer. So, it can prevent bowel cancers too.
From 2016, the bowel screening programme in England will expand to include a one-off flexible sigmoidoscopy test. People will be invited to have this around the time of their 55th birthday. Six bowel cancer screening centres are testing (piloting) this type of screening from 2013. This means if you live near a centre that’s taking part in the pilot, and you are aged between 55 and 60, you may be invited to have this screening test before 2016.
Other countries in the UK are also considering whether to introduce bowel scopes into their bowel cancer screening programmes.
Screening for people at increased risk
If you have an increased risk of bowel cancer, you may be offered bowel screening with a colonoscopy.
The age that colonoscopy screening begins and how often it’s done depends on your estimated risk.
Some people are offered a one-off colonoscopy. If this shows that their bowel is healthy, they won’t need any further colonoscopy screening. But they will still be encouraged to take part in their national bowel cancer screening programme.
When it’s found early, bowel cancer can usually be cured. More than 90% of people (9 out of 10) survive bowel cancer when it’s diagnosed at its earliest stage.
It’s important to be aware of changes that could be a sign of bowel cancer. You should see your GP if you have:
bleeding from your back passage
a change in bowel habit (diarrhoea or constipation) that lasts for more than two weeks
a pain or lump in your tummy
loss of weight or appetite
a feeling of not having emptied your bowel properly after going to the toilet.
Bowel problems are very common, so these symptoms may not be caused by cancer - but it’s important to get them checked out. Don’t be embarrassed to speak to your doctor if you have bowel problems. Conversations like this are part of their everyday work.
It’s important to make another appointment with your GP if the treatment they suggest doesn’t help you.
If you are still worried
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A common reaction to serious illness in the family, or to bereavement, is to feel more vulnerable to the same disease. If you can’t stop worrying, you may find it helpful to speak to a counsellor. You can ask your GP for details of a local counselling service, or contact our cancer support specialists.
The mental health charity MIND has a leaflet called How to Stop Worrying. Order a copy from their website or by calling 0300 123 3393.