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Bowel cancer is a general term that is used to describe cancer that begins in the large bowel. Depending on where in the bowel the cancer starts, bowel cancer can sometimes be referred to as colon cancer, or rectal cancer.

Symptoms of bowel cancer include blood in your stools (faeces), an unexplained change in your bowel habits, such as prolonged diarrhoea or constipation, and unexplained weight loss.

Cancer can sometimes start in the small bowel (small intestine), but small bowel cancer is much rarer than large bowel cancer.

The large bowel

The bowel is part of the digestive system. It has two main purposes:

  • to absorb energy, water, and nutrients from the food you eat, and
  • to pass out the remaining waste products from your body in the form of stools.

The large bowel is made up of five sections which are described below.

  • Ascending colon - runs from the end of the small intestine and up the right-hand side of the abdomen.
  • Transverse colon - runs under the stomach and across the body from right to left.
  • Descending colon - runs down the left-hand side of the abdomen.
  • Sigmoid colon - is an ‘S’ shaped bend that connects the descending colon to the rectum (back passage).
  • Rectum - the final section of the bowel; it is a small pouch that is connected to the outside opening of the bowel (the anus) through which stools are passed.

How does cancer begin?

Cancer begins with an alteration to the structure of the deoxyribonucleic acid (DNA) that is found in all human cells. This is known as a genetic mutation. The DNA provides the cells with a basic set of instructions, such as when to grow and reproduce.

The mutation in the DNA changes these instructions so that the cells carry on growing. This causes the cells to reproduce in an uncontrollable manner, producing a lump of tissue, known as a tumour.

Most cases of bowel cancer first develop inside clumps of cells on the inner lining of the bowel. These clumps are known as polyps. However if you do develop polyps, it does not necessarily mean that you will get bowel cancer.

How does bowel cancer spread?

Bowel cancer can spread through the walls of the bowel into near-by lymph nodes. Lymph nodes are part of the lymphatic system which is spread throughout your body in a similar way to your blood circulation system. The lymph nodes produce many of the specialised cells that are needed by your immune system.

Once the bowel cancer has spread into the lymphatic system, cancerous cells can spread to other parts of the body (metastasis). Bowel cancer usually spreads to the liver, but the lungs, bones, and brain can also sometimes be affected by the cancer.

Risk factors

Exactly what causes cancer to develop inside the bowel is still unknown. However, there is some high quality evidence that has allowed certain risk factors to be identified. These risk factors are explained below.

Family history

There is evidence that bowel cancer can run in families. Around 20 per cent of people who develop bowel cancer have a first degree relative (mother, father, brother, or sister) or a second degree relative (grandparent, uncle, or aunt) who have also had bowel cancer.

It is estimated that if you have one first degree relative with a history of bowel cancer, your risk of getting bowel cancer is doubled. If you have two first degree relatives with a history of bowel cancer, then your risk increases four-fold.


There is a large body of evidence that suggests that a diet that is high in red and processed meat can increase your risk of developing bowel cancer. It is estimated that someone with this type of diet is 35 per cent more likely to develop bowel cancer compared with someone who does not eat red, processed meat.


People who smoke cigarettes are 25 per cent more likely to develop bowel cancer, and other types of cancer and heart disease, compared with people who do not smoke.


Obesity has been linked to an increased risk of bowel cancer. Obese men are 50 per cent more likely to develop bowel cancer compared to a person with a healthy weight. Morbidly obese men (with a body mass index of over 40) are twice as likely to develop bowel cancer.

The risk of obese women developing bowel cancer is lower for reasons that are unclear. Obese women have a very small increased risk of developing the condition, and morbidly obese women are 50 per cent more likely to develop bowel cancer than a person of a healthy weight.

It is uncertain whether this increased risk is directly related to obesity, or to the fact that obese people tend to eat a lot of red and processed meat.

Digestive disorders

There are two digestive disorders that have been linked to an increase risk of cancer:

  • Crohn’s disease - which is a poorly understood condition that causes chronic inflammation of the lining of the digestive system, and
  • ulcerative colitis - another poorly understood condition that causes inflammation of the colon.

People with Crohn’s disease are 2-3 times more likely to develop bowel cancer. Unfortunately, the risk of developing bowel cancer is much higher in people with ulcerative colitis, as 1 in 20 people will go on to develop bowel conditions.

Genetic conditions

There are two rare genetic (inherited) conditions that can cause bowel cancer. They are:

  • familial adenomatous polyposis (FAP), and
  • hereditary non-polyposis colorectal cancer (HNPCC), which is also known as Lynch syndrome.

FAP affects 1 in 10,000 people. The condition triggers the growth of non-cancerous lumps of tissue inside the bowel.

Even though the lumps are non-cancerous, there is a very high risk that, over time, at least one will turn cancerous. Almost all people with FAP will have bowel cancer by the time they are 50 years of age.

Due to the risk, it is usually recommended that a person who is diagnosed with FAP should have their bowel removed as a precaution.

HNPCC is a type of bowel cancer that is caused by a mutated gene that interferes with the DNA’s ability to repair itself. It is estimated that 2-5 per cent of all cases of bowel cancer are due to HNPCC.

Around 90 per cent of men, and 70 per cent of women with the HNPCC mutation will develop bowel cancer by the time they are 70 years of age.

As with FAP, as a precautionary measure, removing the bowel is usually recommended in people with HNPCC.


Your GP will begin the diagnosis by asking you about your pattern of symptoms and whether you have any family history of bowel cancer.

They will then carry out a physical examination that is known as a digital rectal examination (DRE). A DRE involves your GP gently placing their finger into your anus, and then up into your rectum.

A DRE is a useful way of checking whether there is a noticeable lump, or mass, inside your rectum, as this is found in an estimated 40-80 per cent of cases of rectal cancer.

A DRE is not painful procedure, but some people may find it a little embarrassing.

If your symptoms suggest that you may have bowel cancer, or the diagnosis is uncertain, you will be referred to your local hospital for further examination.

Further examination

There are three tests that are used to confirm a diagnosis of bowel cancer:

  • sigmoidoscopy - is an examination of your rectum and some of your large bowel,
  • colonoscopy - is an examination of all of your large bowel, and
  • barium enema - is a type of X-ray that is used to study your bowel in more detail.


A sigmoidoscopy uses a device called a sigmoidoscope, which is a thin, flexible tube that is attached to a small camera and light.

The sigmoidoscope is inserted into your rectum and then up into your bowel. The camera relays images to a monitor that allows the doctor to check for any abnormal areas within the rectum or bowel that could be the result of cancer.

A sigmoidoscopy can also be used to remove small samples of suspected cancerous tissue so that they can be tested in a libratory. This is known as a biopsy.

A sigmoidoscopy is not usually painful, but it can feel slightly uncomfortable. Most people are able go home after the examination has been completed.


A colonoscopy is a similar examination to a sigmoidoscopy apart from a larger tube, called a colonoscope, is used to examine your entire bowel.

Your bowel needs to be empty when a colonoscopy is performed, so you will be given a special diet to eat for a few days before the examination and a laxative (medication to help empty your bowel) on the morning of the examination.

You will be given a sedative to help you relax after which the doctor will insert the colonoscope into your rectum, and move it along the length of your large bowel. As with a sigmoidoscope, the colonoscope can be used to obtain a biopsy, as well as relaying images of any abnormal areas.

A colonoscopy usually takes about one hour to complete, and most people are able to go home once they have recovered from the effects of the sedative. After the procedure, you will probably feel a bit drowsy for a while so you should arrange for someone to accompany you home.

Barium enema

As with a colonoscopy, a barium enema also has to be performed when your bowel is empty, so you will be asked not to eat or drink anything on the morning of the procedure, and you will be given a laxative to take.

Before the examination begins, a nurse may wash out your bowel by placing a tube into your rectum and up into your bowel. Water will then be passed into your bowel.

A barium enema is performed in much the same way as washing out your bowel. Barium is a special type of liquid that shows up clearly on X-rays.

During a barium enema, barium is pumped into your bowel and, afterwards, a doctor will study how it moves through your bowel on an X-ray. This is useful for spotting any unusual lumps, masses, or blockages in your bowel.

A barium enema takes around 15-20 minutes to complete and, afterwards, you should be able to go home. You may experience some stomach cramping for a few hours after the enema has been completed. However, this is normal and it is nothing to worry about.

You will be advised to drink plenty of fluids as this will help to wash the barium out of your bowel.
Your stools will have a white-grey appearance for a few days, but they should return to their usual colour soon afterwards.

Further testing

If a diagnosis of bowel cancer is confirmed, further testing is usually carried out for two reasons:

  • to check if the cancer has spread from the bowel to other parts of the body, and
  • to help decide what will be the most effective treatment for you.

These tests can include:

  • a computerised tomography (CT) scan, or magnetic resonance imaging (MRI) scan - to provide a detailed image of your colon,
  • ultrasound scans - which can be used to look inside other organs, such as your liver, to see if the cancer has spread there,
  • chest X-rays - which can be used to assess the state of your heart and lungs, and
  • blood tests - in some cases of bowel cancer, the cancerous cells release a special protein, known as a tumour marker, which can be detected with a blood test.

Staging and grading

Once the above examinations and tests have been completed, it should be possible to determine what stage and grade your cancer is. Staging refers to how far your cancer has advanced, and grading relates to how aggressive, and likely to spread, your cancer is.

A staging system called the Dukes system is usually used to stage bowel cancer which has four stages measured from A-D.

  • Dukes A - the cancer is still contained within the lining of the bowel or rectum.
  • Dukes B - the cancer has spread into the layer of muscle surrounding the bowel.
  • Dukes C - the cancer has spread into near by lymph nodes.
  • Dukes D - the cancer has spread into another part of the body, such as the liver.

There are three grades of bowel cancer:

  • grade one - is a cancer that grows slowly and has a low chance of spreading beyond the bowel,
  • grade two - is a cancer that grows moderately and has a medium chance of spreading beyond the bowel, and
  • grade three - is a cancer that grows rapidly and has a high chance of spreading beyond the bowel.

Many primary care trusts (PCTs) have multi-disciplinary teams (MDTs) that treat bowel cancer.

A MDT is made up of a number of different specialist including:

  • a gastroenterologist surgeon (a specialist in bowel surgery),
  • a clinical oncologist (a specialist in the non-surgical treatment of cancer),
  • a pathologist (a specialist in diseased tissue),
  • a radiologist (a specialist in radiotherapy),
  • a social worker,
  • a psychologist,
  • a palliative care specialist (a doctor, or nurse, with special training in providing pain relief), and
  • a specialist cancer nurse, who will usually be your first point of contact with the rest of the team.

If you have bowel cancer, you may see several, or all, of these healthcare professionals as part of your treatment.

Deciding what treatment is best for you can be difficult. Your cancer team will make recommendations, but the final decision will be yours.

Before going to hospital to discuss your treatment options, you may find it useful to write a list of questions to ask the specialist. For example, you may want to find out what the advantages and disadvantages of particular treatments are.

Your treatment plan

Your recommended treatment plan will depend on the stage and location of your bowel cancer.
If the cancer is confined to your rectum, radiotherapy will be used to shrink the tumour, and then surgery may be used to remove the tumour. Sometimes, radiotherapy is combined with chemotherapy, which is known as chemoradiation.

If you have Dukes A bowel cancer, it should be possible to surgically remove the cancer and no further treatment will be required.

If you have Dukes B, or C, bowel cancer, surgery may be used to remove the cancer and, in some cases, near by lymph nodes. Surgery is usually followed by a course of chemotherapy in order to prevent the cancer returning.

It is not usually possible to cure Dukes D cancer. However, the symptoms can be controlled and the spread of the cancer can be slowed using a combination of chemotherapy, radiotherapy, surgery, and a new type of medication called cetuximab (Erbitux).


There are two main ways that radiotherapy can be used to treat bowel cancer. It can be:

  • given before surgery, in cases of rectal cancer, and
  • used to control symptoms and slow the spread of cancer, in cases of advanced bowel cancer (palliative radiotherapy).

Radiotherapy given before surgery for rectal cancer can be performed in two ways:

  • external radiotherapy - where a machine is used to beam high energy waves at your rectum in order to kill cancerous cells, and
  • internal radiotherapy (also known as brachytherapy) - where a radioactive tube is inserted into your anus and placed next to the tumour in order to shrink it.

Research suggests that people who are treated with internal radiotherapy are less likely to need to have their entire rectum and anus removed and will not need to have a permanent colostomy (where a section of the colon is diverted and attached to an opening in the abdominal wall called a stoma) See below for more information about colostomies.

However, as internal radiotherapy is a relatively new treatment, there is no information about how successful it is in the long-term in prolonging life and preventing cancer returning.

You should discuss the advantages of both types of radiotherapy treatment with your care team.

External radiotherapy is usually given on a daily basis, five days a week, with a break at the weekend. Depending on the size of your tumour, you may need 1-5 weeks of treatment. Each session of radiotherapy is short and will only last for between 10-15 minutes.

Internal radiotherapy can usually be performed in one session before surgery is carried out a few weeks later.

Palliative radiotherapy is usually given in short, daily sessions, with a course ranging from 2-3 days to 10 days.

Short term side effects of radiotherapy:

  • nausea,
  • fatigue,
  • diarrhoea,
  • burning and irritation of the skin around the rectum and pelvis (this looks and feels like sunburn),
  • a frequent need to urinate, and
  • a burning sensation when passing urine.

These side effects should pass once the course of radiotherapy has finished. You should tell your care team if the side effects of treatment become particularly troublesome. Additional treatments are often available to help you cope better with the side effects.

Long term side effects of radiotherapy include:

  • a more frequent need to pass urine or stools,
  • blood in your urine and stools,
  • infertility, and, in men,
  • impotence.

If you wish to have children it may be possible to store a sample of your sperm (or eggs) before treatment begins so that they can be used in fertility treatments in the future.

Medications such as sildenafil (Vigra) can be used to treat some cases of impotence.

Surgery - colon cancer

If the cancer is at a very early stage, it may be possible to remove just a small piece of the lining of the colon wall. This is known as local excision.

If the cancer has begun to spread into the muscles surrounding the colon, it will usually be necessary to remove an entire section of your colon. Removing some of the colon is known as a colectomy.

Depending on the location of the cancer, possible surgical procedures include:

  • left-hemi colectomy - where the left half of your colon is removed,
  • transverse colectomy - where the middle section of your colon is removed,
  • right-hemi colectomy - where the right half of your colon is removed, and
  • sigmoid colectomy - where the lower section of your colon is removed.

There are two ways that a colectomy can be performed:

  • an open colectomy - where the surgeon makes a large incision in your abdomen and removes a section of your colon, or
  • laparoscopic colectomy  - a type of ‘keyhole surgery’ where the surgeon makes a number of small incisions in your abdomen and uses special instruments guided by a camera to remove a section of colon.

Both techniques are thought to be equally effective in removing cancer and have similar risks of complications. Laparoscopic colectomies have the advantage of having a faster recovery time and causing less post-operative pain.

Laparoscopic colectomies are a new technique so they may only be available at specialist cancer clinics, and there may be a longer waiting time for this type of surgery.

During surgery, near-by lymph nodes may also be removed. In some cases, it will be possible to reconnect the remaining sections of the colon.

Stoma surgery

In some cases, the surgeon may decide that the colon needs to heal before it can be reattached, or that too much of the colon has been removed to make reattachment possible.
It will therefore be necessary to find a way of removing wasting materials from your body without using all of your colon. This is done using stoma surgery.

Stoma surgery involves the surgeon making a small hole in your abdomen that is known as a stoma. There are two ways that stoma surgery can be carried out. These are explained below.

  • An ileostomy - where a stoma is made in the right-hand side of your abdomen. Your small intestine is separated from your colon and connected to the stoma, and the rest of the colon is sealed. You will need to wear a pouch that is connected to the stoma to collect waste material.
  • A colostomy - where a stoma is made in your lower abdomen and a section of the colon is removed and connected to the stoma. As with an ileostomy, you will need to wear a pouch to collect waste material.

In most cases, the stoma will be temporary and can be removed once your colon has recovered from the effects of the surgery. This will usually take at least nine weeks.

If most of your colon needs to removed in order to fully eliminate the cancer, it may be necessary to have a permanent ileostomy or colostomy.

Before you have a colectomy, your care team will be able to tell you whether they think that stoma surgery will be necessary and the likelihood that you will need to have a temporary or permanent ileostomy or colostomy.

Surgery - rectal cancer

There are three surgical procedures that can be used to treat rectal cancers:

  • low anterior resection,
  • colo anal anastomosis, and
  • abdominoperineal resection.

These procedures are explained below.

Low anterior resection

Low anterior resection is a procedure that is used to treat cases where the cancer is in the upper section of your rectum. The surgeon will make an incision in your abdomen and remove the upper section of your rectum as well as some surrounding tissue. They will then attach your colon to the remainder of your rectum.

Colo anal anastomosis 

Colo anal anastomosis is used to treat cases where the cancer is in the middle section of your rectum. During the procedure, the surgeon will remove most of your rectum. They will then take a small section of your rectum and reconstruct it into a pouch which will act as an ‘artificial rectum’. The pouch is then connected to your anus. You will probably require a temporary colostomy to allow time for your bowel to heal.

Abdominoperineal resection

Abdominoperineal resection is used to treat cases where the cancer is in the lower section of your rectum. In this case, it will be necessary to remove a large section of your rectum. As there will not be enough rectum left to function properly, it will also be necessary to remove your anus and for you to have a permanent colostomy.


There are three ways that chemotherapy can be used to treat bowel cancer. It can be:

  • given before surgery for rectal cancer in combination with radiotherapy,
  • given after surgery to prevent the return of cancer, and
  • given to slow the spread of advanced bowel cancer and can help to control symptoms (palliative chemotherapy).

Chemotherapy for bowel cancer usually involves taking a combination of cancer cell killing medications. They can be given in tablet form (oral chemotherapy), or through a drip in your arm or chest (intravenous chemotherapy), or with a combination of both.

Depending on the stage and grade of your cancer, a single session of intravenous chemotherapy can last from several hours to several days.

Most people have regular daily sessions of chemotherapy over the course of one or two weeks before having a break from treatment for another week.

A course of chemotherapy can last up to six months depending on how well you respond to the treatment.

Side effects of chemotherapy include:

  • fatigue,
  • nausea,
  • vomiting,
  • diarrhoea,
  • mouth ulcers,
  • hair loss,
  • redness and soreness on the palms of your hands and the soles of your feet, and
  • a sensation of numbness, tingling and/or burning in your hands, feet, and neck.

These side effects should gradually pass once your treatment has finished. It usually takes between 3-6 months for your hair to grow back.

Chemotherapy can also weaken your immune system, making you more vulnerable to infection. You should inform your care team and/or your GP as soon as possible if you experience the possible signs of an infection such as:

  • a high temperature (fever) of 38ºC (100.4ºF), or above, and/or
  • a sudden feeling of being generally unwell.

The medications that are used in chemotherapy can temporary damage sperm (in men) and eggs (in women). This means that for women who become pregnant, or for men who father a child, there is a risk to the unborn baby’s health. It is therefore recommended that you use a reliable method of contraception while having chemotherapy treatment and for a further year after your treatment has finished.


Cetuximab is a new type of medication known as monoclonal antibodies. Monoclonal antibodies are antibodies that have been genetically engineered in a laboratory.

Cetuximab targets special proteins that are found on the surface of cancer cells, known as epidermal growth factor receptors (EGFR). As EGFRs help the cancer to grow, by targeting these proteins, cetuximab can help prevent the cancer spreading. It is usually used in combination with chemotherapy and radiotherapy.

Cetuximab is only available on the NHS when:

  • bowel cancer has spread to the liver and cannot be removed using surgery,
  • surgery to remove the cancer in the colon, or rectum, has been carried out or is possible, and
  • a person is fit enough to undergo surgery to remove the cancer from the liver if this becomes possible after treatment with cetuximab.

Cetuximab is available on a private basis, but the medication is very expensive. It is usually given in combination with chemotherapy.

Cetuximab is given through a drip into your vein, which slowly administers the first dose over the course of a few hours. After this, further doses are given on a weekly basis and they should only take an hour.

The most common side effect of cetuximab is the development of an acne-like rash in the skin which occurs in about 80 per cent of cases.

Other side effects of cetuximab include:

  • nausea,
  • diarrhoea,
  • breathlessness, and
  • conjunctivitis (inflammation of the eyes)

Cetuximab has been known to trigger allergic reactions in some people, such as a swollen tongue or throat. Occasionally, these allergic reactions can be severe and life-threatening. This is known as an infusion reaction. Infusion reactions occur in about three per cent of people receiving cetuximab.

Most infusion reactions occur within the first 24 hours of someone beginning treatment. You will therefore be closely monitored when your treatment begins. If you start to experience symptoms of an infusion reaction, anti-allergy medicines, such as corticosteroids, can be used to relieve them.

Due to these precautionary measures, deaths from infusion reactions in people who are taking cetuximab are very rare, occurring in less than 0.1 per cent of cases.


The initial symptoms of bowel cancer include:

  • blood in your stools (faeces) and/or bleeding from your rectum,
  • a change to your normal bowel habits that persists for more than six weeks, such as diarrhoea, constipation, or passing stools more frequently than usual,
  • abdominal pain, and
  • unexplained weight loss.

As bowel cancer progresses, it can sometimes cause bleeding inside the bowel which eventually will mean that your body will not have enough red blood cells. This is known as anaemia.

Symptoms of anaemia include:

  • fatigue, and
  • breathlessness.

In some cases, bowel cancer can cause an obstruction in the bowel. Symptoms of a bowel obstruction include:

  • a feeling of bloating, usually around the navel (belly button),
  • abdominal pain,
  • constipation, and
  • vomiting.

When to seek medical advice

You should always contact your GP if you experience any of the symptoms that are listed above. While the symptoms are unlikely to be the result of bowel cancer, these types of symptoms always need to be investigated further.