Bowel cancer

How cancer develops

About bowel cancer

Bowel cancer is the third most common cancer in the UK. About five in 100 people will develop bowel cancer in the UK. You can get bowel cancer at any age but 80 out of 100 people who develop bowel cancer are over the age of 60.

Bowel cancer, also known as colorectal cancer, is the name for any cancer of your large bowel and back passage (rectum). Very rarely, cancers can occur in your small bowel.

Your large bowel (also called your colon) is the last section of your digestive system. Food passes through your small bowel (the longer, thinner part of your bowel) where nutrients are absorbed. Food waste then travels through your large bowel, where it becomes more solid faeces.

Your large bowel is divided into several sections including: the ascending; transverse; and descending colon. Your rectum, at the end of your large bowel, is where faeces collects before passing through your anus as a bowel movement.

Usually, large bowel cancers develop from small, non-cancerous (benign) growths of tissue called polyps that can extend from the lining of your bowel wall. Sometimes polyps can become cancerous (malignant) over time. If the cancer isn't treated, it can grow through the wall of your bowel and spread to other parts of your body.

Symptoms of bowel cancer

Bowel cancer is often painless in the early stages, but there are symptoms, including:

  • blood in your faeces, which may be mixed into your faeces or appear as flecks on the surface, or you may see it in the toilet or on toilet paper – get into the habit of looking into the toilet before flushing
  • persistent changes in your bowel habit for several weeks – especially going to the toilet more often or having diarrhoea
  • weight loss without any obvious reason and/or loss of appetite
  • tiredness or breathlessness for no apparent reason – this may be caused by the small amount of blood loss from your bowel, resulting in anaemia (when there are too few red blood cells or not enough haemoglobin in your blood)
  • pain, or a lump or swelling in your abdomen (tummy)

These symptoms aren't always caused by bowel cancer. For example, problems such as piles may cause blood to appear in your faeces. However, if you have any of these symptoms, see your GP.

Causes of bowel cancer

The causes of bowel cancer aren't fully understood at present.

Your risk of bowel cancer increases if you have:

  • a family history of bowel cancer
  • one of two inherited bowel conditions that increase your risk – familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer (HNPCC), also known as Lynch syndrome
  • a long-term bowel condition, such as Crohn's disease or ulcerative colitis
  • a diet that is low in fibre, fruit and vegetables and high in red and processed meats
  • an inactive lifestyle or are obese
  • diabetes

You’re also more likely to get bowel cancer as you get older.

Diagnosis of bowel cancer

Your GP will ask about your symptoms and examine you. This may include a rectal examination to feel for any lumps or swellings in your back passage. He or she may also ask you about your medical history. Your GP may refer you to a doctor or surgeon who specialises in colorectal disease.

Tests for bowel cancer include the following.

  • A colonoscopy. This is a test that allows a doctor to look inside your large bowel. The test is done using a narrow, flexible, tube-like telescopic camera called a colonoscope.
  • A sigmoidoscopy. This is a procedure used to look inside your rectum and the lower part of your bowel.
  • A barium enema. This involves placing a fluid containing barium (a substance which shows up on X-rays) into your bowel via your rectum. X-ray images of your abdomen then show the inside of your bowel more clearly.
  • A virtual colonoscopy. Instead of having a colonoscope put inside your bowel, a CT scan is used to create a three-dimensional image of the inside of your bowel. This is a newer test that may not be available in all hospitals.

If your doctor diagnoses bowel cancer, you may need further tests to find the size and position of the cancer.

These tests may include:

  • an ultrasound scan of your abdomen to see if the cancer has spread
  • a CT scan to show the position of the tumour
  • an MRI scan to show two- and three-dimensional pictures of your bowel
  • a chest X-ray to check the health of your heart and lungs
  • blood tests to assess your general health

Screening for bowel cancer

Screening is important for detecting bowel cancer in its early stages. The Department of Health has introduced a bowel cancer screening programme in England. Bowel cancer screening kits are sent to men and women aged between 60 and 69, although if you're older you can also request a kit. There are different programmes running in the rest of the UK. Ask your GP whether the screening programme has started in your area.

The screening kit contains a faecal occult blood (FOB) test that can detect small amounts of blood in your faeces. The FOB test doesn't diagnose bowel cancer, but the results show if you need to have your bowel examined.

Some people who are more likely to develop bowel cancer can also be screened. You may choose to have regular screening if you:

  • are over 60 years old
  • have a close relative who has had bowel cancer
  • have familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer (HNPCC), or other diseases of the bowel lining such as ulcerative colitis or Crohn's disease

Treatment of bowel cancer

The type of treatment you have will depend on the size of the tumour, its position and whether it has spread.


Surgery is the most common treatment for bowel cancer.

If you have surgery, the part of your large bowel that contains the cancer will be removed and the two open ends are usually joined together. Lymph nodes (glands found throughout your body that are part of your immune system) near your bowel are often removed as well because they are the first place the cancer usually spreads to.

Sometimes, depending on the location and size of the cancer that is removed, the two ends of your bowel can't be rejoined. If this happens, the opening nearest the beginning of your bowel will be brought out to the skin surface of your abdomen. A colostomy is an opening of your large bowel onto the surface of your abdomen and an ileostomy is an opening of your small bowel onto the surface of the abdomen. The opening of the bowel is known as a stoma. See our common questions for more information.

A bag is worn over the stoma, which collects your bowel movements outside your body. Most people who have surgery don't need a colostomy, but if you do, it's usually temporary.

If you have cancer in your rectum, you may need surgery to remove the part of your rectum that contains the cancer, as well as the fatty tissue and lymph nodes around your rectum. You're more likely to need a colostomy if you have cancer of the rectum than if you have cancer of the colon.

Non-surgical treatments

Chemotherapy and radiotherapy

Sometimes it's not possible to remove all the cancer by surgery, so you may need to have additional treatment with chemotherapy and/or radiotherapy.

These treatments aim to destroy any remaining cancer cells and to prevent the cancer spreading further. Chemotherapy and radiotherapy are also sometimes used to shrink the tumour, before or after surgery, to kill any cancer cells that might be left after surgery or to help reduce your symptoms.

Chemotherapy aims to destroy cancer cells with medicines. These medicines may be given through a drip into your bloodstream (intravenous), as injections or as tablets or capsules that you swallow.

Radiotherapy uses X-rays to kill cancer cells. It’s often used to treat cancer that has started in the back rectum.

Chemotherapy and radiotherapy can both have side-effects.

Monoclonal antibodies

Less commonly used are monoclonal antibodies that are medicines designed to recognise specific proteins on cancer cells. There are three main monoclonal antibodies used in the treatment for bowel cancer:

  • bevacizumab
  • cetuximab
  • panitumumab

These medicines seek out cancer cells and stop them growing. They are sometimes used alongside chemotherapy. They can be used for various stages of cancer – ask your doctor for more advice.

Prevention of bowel cancer

There is evidence that taking the following steps can help to reduce your risk of getting bowel cancer.

  • Try to do 150 minutes (two and a half hours) of moderate exercise over a week in bouts of 10 minutes or more. You can do this by carrying out 30 minutes on at least five days each week. Alternatively, you can do 75 minutes of vigorous intensity activity twice a week.
  • Eat five or more portions of fruit and vegetables every day.
  • Cut down on the amount of processed meat and red meat you eat.
  • Maintain a healthy weight.
  • Eat foods high in fibre such as wholegrain bread, cereals and pasta.
  • If you smoke, stop.
  • Drink alcohol in moderation – no more than two to three units a day for women and three to four units a day for men.

There is increasing evidence that vitamin D may help to reduce your risk of bowel cancer, but more research needs to be done to be certain. Read more about how vitamin D may protect against cancer.  

Why are people with bowel conditions such as Crohn's disease and ulcerative colitis more likely to develop bowel cancer?


Inflammatory bowel diseases, such as Crohn's disease or ulcerative colitis, are thought to cause damage to the lining of your bowel over a long period of time. This could make you more likely to develop bowel cancer.


Crohn's disease and ulcerative colitis are both chronic diseases that cause your bowel to become inflamed. A chronic illness is one that lasts a long time, sometimes for the rest of your life. When describing an illness, the term chronic refers to how long a person has it, not to how serious a condition is.

It's thought that over time the damage caused to the lining of your bowel increases the risk of cancerous cells developing. Research suggests that if you have had symptoms of Crohn's disease or ulcerative colitis and it has affected your entire bowel for more than eight years then you're at a higher risk of bowel cancer than the average person. If only the left-hand side of your colon is affected by ulcerative colitis or only your small intestine is affected by Crohn’s disease, your risk of developing bowel cancer is lower.

It has been estimated that bowel cancer is caused by ulcerative colitis in about one in every 100 people diagnosed with bowel cancer.

If you have Crohn's disease or ulcerative colitis, you may be offered regular bowel cancer screening. If you have had your condition for between 10 and 20 years, it's recommended that you should be screened every three years. When you have had it for between 20 and 30 years this will be increased to every two years. After 30 years you will be screened every year. Your doctor will advise you on what is recommended and why.

Screening may involve having a faecal occult blood (FOB) test to detect small amounts of blood in your faeces or a colonoscopy. A colonoscopy is a test that allows a doctor to look inside your large bowel. The test is done using a narrow, flexible, tube-like telescopic camera called a colonoscope. This type of screening means that if you do develop bowel cancer, it can be detected and treated early.

If you have any questions about Crohn's disease, ulcerative colitis or bowel cancer, talk to your GP.

Can calcium help reduce the risk of developing bowel cancer?


Possibly. Research has suggested that people who have more calcium in their diet are less likely to develop polyps in their bowel. Polyps are growths in the bowel that may develop into cancer over a long period of time. However, no research has directly shown that taking calcium supplements has any effect on your risk of getting bowel cancer.


Calcium is an important part of your diet. It helps build strong bones and teeth, regulates your muscle contractions (including your heartbeat) and makes sure your blood clots normally. More recently, research has suggested that it may also help prevent certain cancers, including bowel cancer.

Studies have found that people who have high amounts of calcium in their diet may be less likely to develop bowel cancer than those who have little calcium in their diet. On average, adults needs around 700 milligrams (mg) of calcium per day. The research found that taking 1,200 milligrams (mg) of calcium supplements a day helps to prevent polyps (growths) developing in your large bowel. These polyps are dangerous because over time they can change and become cancerous.

So far, these findings have only shown that calcium supplements may contribute to the prevention of bowel polyps. More research needs to be done to establish whether increasing calcium in your diet prevents bowel cancer.

It's important to make sure that you're getting enough calcium in your diet to keep you healthy and prevent long-term health conditions. Good sources of calcium include milk, cheese and other dairy products, green leafy vegetables (such as broccoli), soya products, nuts and anything made with fortified flour.

At this stage, it's too early to say whether extra calcium in your diet will help protect against bowel cancer. Ask your GP for more information about how your diet may affect your risk of developing bowel cancer.

What is the difference between a colostomy and an ileostomy?


A colostomy and ileostomy are both surgical procedures that involve bringing part of your bowel to your abdomen (tummy) wall to create an artificial opening (stoma). The difference between them is in the part of the bowel that the stoma joins. A colostomy is when your large bowel is joined to the opening, whereas an ileostomy is when your small bowel is joined to the opening.


Procedures with a name ending in 'ostomy' usually involve part of your bowel being joined to an artificial opening called a stoma in your abdomen. The first part of the word refers to the part of the bowel affected, ie 'col' in the word colostomy refers to your colon (large bowel) and 'ile' in ileostomy refers to your ileum (small bowel). A bag is worn over the stoma to collect bowel movements. The stoma is usually placed low down on your abdomen so it's hidden under your clothing.

An ileostomy is an opening from the small bowel, to allow faeces to leave your body without passing through your large bowel. A colostomy is an opening from your large bowel to allow faeces to leave your body without passing through your anus.

These procedures are carried out if parts of your bowel can't be rejoined after having surgery for conditions such as Crohn's disease, bowel cancer or diverticulosis. A colostomy is usually temporary when used after surgery for bowel cancer. An operation is normally carried out a couple of months after your initial treatment to rejoin your bowel and remove the stoma. This is called a stoma reversal. Occasionally, if your bowel can't be rejoined, the stoma is permanent.

Having a stoma can be both physically and mentally challenging. However, most people are able to carry on with their lives as they did before and participate in activities such as swimming. There are patient support group’s available, such as the Colostomy Association and the Ileostomy and Internal Pouch Support Group that can provide support and advice on having a stoma.

If you have any questions or concerns about colostomy or ileostomy, talk to your surgeon, GP or nurse.