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A quick guide to what's on this page

How common is bowel cancer?

Bowel (colorectal) cancer is the 4th most common cancer in the UK. Most bowel cancers are in the large bowel (the colon), with about 1 in 3 in the back passage (rectum). We don't know the exact cause of bowel cancer in most cases. More than 8 out of 10 bowel cancers (80%) are diagnosed in people aged 60 or over.

Family history and inherited conditions

A strong family history means you have several relatives on the same side of your family diagnosed with bowel cancer, or one or more relatives diagnosed at a young age. If you think you have a strong family history, see your GP. They may refer you to a specialist genetics service. 

About 1 in 20 cases of bowel cancer (5%) are caused by inherited conditions called familial adenomatous polyposis (FAP) and hereditary non polyposis colorectal cancer (HNPCC or Lynch syndrome). People who have an Ashkenazi Jewish background also have a higher risk of bowel cancer.

Medical conditions that increase risk

Growths in the bowel called polyps or adenomas can develop into cancer over a long period of time. Adenomas are quite common, but only a small fraction of them become cancer. Having ulcerative colitis or Crohn's disease for many years increases your risk of bowel cancer. Diabetes and some other medical conditions also increase the risk, though we don’t know why. You are at higher risk of bowel cancer if you have had it before, or if you have had womb cancer, testicular cancer, or lymphoma.

 

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How common bowel cancer is in the UK

Bowel (colorectal) cancer is the 4th most common cancer in the UK after breast, lung and prostate cancer. In the UK around 41,600 people are diagnosed with bowel cancer each year.

 

Bowel cancer and age

The biggest single risk factor is age. More than 8 out of 10 bowel cancers (80%) are diagnosed in people aged 60 or over. So the risk increases as you get older. The page about how a cancer starts explains why cancers are more likely as we get older. But we think that many bowel cancers could be prevented with changes in diet and lifestyle. You can find more information about this on the pages about diet as a risk factor for bowel cancer and other lifestyle risk factors.

 

A family history of bowel cancer

A strong family history usually means you have several relatives diagnosed with bowel cancer, especially if they are in different generations of your family. It can also mean you have one or more relatives diagnosed at a particularly young age. Examples of a strong family history are

  • 1 first degree relative diagnosed before the age of 45
  • 2 first degree relatives diagnosed at any age

A first degree relative is a parent, brother or sister, son or daughter. To have a strong family history, the affected relatives must all come from the same side of your family.

If you think you have a strong family history of bowel cancer, see your GP. If your doctor agrees, they will probably refer you to a specialist genetics service. They will look into your background closely by talking through your family history and asking detailed questions about your family's health and illnesses. You may have blood tests as part of this investigation. 

If the geneticist agrees that you do have a higher than average risk of bowel cancer, you'll then see a bowel specialist. The bowel specialist will talk to you about having regular tests (screening) to pick up any signs of cancer as early as possible. There is information about screening people at high risk of bowel cancer in this section.

 

The inherited conditions FAP and HNPCC

Two inherited conditions can increase bowel cancer risk. These are FAP and HNPCC. FAP stands for familial adenomatous polyposis. HNPCC stands for hereditary non polyposis colorectal cancer (also called Lynch syndrome). These gene changes increase the risk quite a bit for people who have them, but they are very rare. FAP and HNPCC together are only responsible for about 1 in 20 cases of bowel cancer (5%).

FAP

FAP (familial adenomatous polyposis) is a rare disease that runs in families. It is responsible for about 1 out of every 100 bowel cancers (1%). FAP causes lots of small non cancerous growths (benign polyps) to develop in the large bowel. Some of these can develop into cancer over a long period of time. Because people with FAP have so many polyps, they have a high risk of getting bowel cancer. By their 40s or 50s, it is almost certain they will have bowel cancer. Specialists recommend that people with FAP have surgery by age 25 to remove all of their colon and prevent them getting bowel cancer. There is information about this on the page about screening people with FAP.

You can have FAP even if there are no other cases in your family. The gene mutation comes about by accident in about 1 in 4 cases (25%) and not because you've inherited it.

HNPCC

Another rare gene fault that runs in some families is Lynch syndrome or HNPCC (hereditary non polyposis colorectal cancer). The healthy form of this gene helps DNA to repair itself. If you have the faulty gene for HNPCC, you are at a greater risk of several different cancers. Bowel cancer risk is increased most. But there is also an increased risk of womb cancer, ovarian cancer, stomach cancer, pancreatic cancer, biliary cancer, and bladder cancer. About 9 out of 10 men (90%) and 7 out of 10 women (70%) with the HNPCC gene fault develop bowel cancer by age 70. If your doctor suspects that you carry an HNPCC gene fault, your specialist may suggest surgery to try to stop bowel cancer developing.

Because it is rare, HNPCC is probably only responsible for between 1 and 4 out of every 100 bowel cancers diagnosed (1 to 4%). If you have a relative with this particular gene fault, you can be tested to see if you have it too. But at the moment, it is not possible to genetically screen everyone in the population.

HNPCC is particularly linked to bowel cancer that develops at a young age. It probably causes about 4 out of 10 bowel cancer cases (40%) in people under 30. A Cancer Research UK study in Scotland is screening everyone under 55 with bowel cancer, to see if they carry the gene fault. Once this study is complete, relatives of people who carry the gene fault can be tested. There is information about screening for people with HNPCC on the page about who is screened for bowel cancer.

 

Being Ashkenazi Jewish

People with an Ashkenazi Jewish background have a higher risk of bowel cancer. This may be due to a gene fault that is more common in this group. About 1 in 10 Ashkenazi Jews have a faulty gene called I1307K. We don't know yet if it is this gene that causes the increase in bowel cancer. People in this ethnic group also have a higher risk of breast cancer because they are more likely to carry one of the breast cancer gene faults – BRCA1 or BRCA2.

 

Benign polyps in the bowel

Growths in the bowel, called polyps or adenomas, are not cancerous. But they can develop into cancer over a long period of time. In fact, most bowel cancers develop from an adenoma. Adenomas are quite common. About 1 in 4 (25%) of us have at least one polyp by age 50. About half of us have them by age 70. But only a small fraction of adenomas develop into cancer and it takes years to happen. 

An adenoma that is 1 cm across has roughly a 1 in 6 chance of growing into a cancer over 10 years. The bowel cancer screening programmes in England, Wales, Scotland and Northern Ireland aim to find and remove polyps in the general population before they become cancerous. People with gene changes that increase bowel cancer risk may need to have screening more often than the general population. In this section there is detailed information about screening people at high risk of bowel cancer.

 

Ulcerative colitis and Crohn's disease

Ulcerative colitis and Crohn's disease are chronic bowel diseases causing inflammation in the bowel. Having either of these diseases for many years increases your risk of bowel cancer. The level of risk depends on a number of different factors. Probably about 1 in every 100 cases of bowel cancer (1%) is due to ulcerative colitis. 

The increased cancer risk is probably because the disease damages the lining of the bowel and it has to repair itself again and again. The increase in cell turnover increases the risk that a cancerous cell might develop. You can read about screening people with a history of ulcerative colitis and Crohn's in this section.

 

Having had cancer before

If you have already had bowel cancer, you have an increased risk of getting it again. Your specialist will talk to you about how often you may need screening. There is more information about this on the page about who can be screened for bowel cancer.

Studies also show that people who have had lymphoma, testicular cancer or womb cancer (endometrial cancer) have an increased risk of bowel cancer. This may be due to genetic changes or could be an effect of the treatment for the first cancer.

 

Bowel cancer and other medical conditions

If you have diabetes, your pancreas doesn't make enough of a hormone called insulin. People with diabetes have an increased risk of bowel cancer. We don't know why this is and scientists are looking into it.

Studies show an increased risk of bowel cancer in people who have had an organ transplant. 

People with acromegaly also have an increased risk. Acromegaly is a condition where the pituitary gland produces too much growth hormone and causes an overgrowth of bones, especially in the face. 

Some studies have shown that people who have had their gallbladder removed (cholecystectomy) have an increased risk of bowel cancer. But other studies have not shown this link.

 

Radiation

It is estimated that about 1 in 100 cases of bowel cancer in the UK (1%) are linked to radiation exposure. Some of these cases are due to radiotherapy treatment for a previous cancer. The rest are linked to radiation used in tests such as X-rays and CT scans (diagnostic radiation) and background radiation.

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Updated: 14 January 2014