Colorectal cancer

Colorectal cancer is the 4th most common cancer in the UK, with over 42,000 people diagnosed every year.

In this section

The bowel is part of the digestive system stretching from the stomach to the anus. It is a hollow tube coiled up in your abdomen, divided into two parts: the small bowel and the large bowel (the colon and the rectum). Cancer in the large bowel is known as colorectal cancer.

Causes of colorectal cancer

Unfortunately we still know very little about the causes of cancer of the large bowel, also called colorectal cancer. However, studies have shown that the frequency of bowel cancer is greater in countries which eat a diet high in fat and low in fibre (roughage). It has been suggested that a high alcohol intake, particularly of beer, may be linked to this cancer.

There are two inherited conditions that can increase the risk of developing colorectal cancer. They are Familial Adenomatous Polyposis (FAP) and Hereditary Non-Polyposis Colon Cancer (HNPCC). Together, they account for 5% of bowel cancers.

A history of severe ulcerative colitis or Crohn’s disease affecting the large bowel may also increase the risk of developing colorectal cancer.


The commonest symptom of colorectal cancer is a change of bowel habits. There may be increasing constipation, or perhaps alternating bouts of constipation and diarrhoea. There may be blood or mucus in the stools. A feeling that you haven't completely emptied your bowels is quite common if the tumour is in the rectum. This can be uncomfortable and you may constantly feel the urge to go to the toilet.

You may feel a colicky type pain, or vague discomfort in your abdomen. You may also feel generally unwell, for example listless or tired, because you have been losing blood from the bowel and may have become anaemic (lack of red blood cells).

If your symptoms have lasted six or more weeks, including bleeding from the rectum, you need to see a specialist.

Colorectal cancer diagnosis

There are a series of tests and investigations which can be done to confirm or rule out a diagnosis of colorectal cancer, and to find out whether the cancer has spread to other parts of your body.

There are several ways which the doctor can examine your bowel. Whatever examination is used your bowel will need to be prepared. It must be as empty as possible so that the doctor can get a clear view inside.

The preparation may vary but will usually include:

  • eating a low fibre (roughage) diet for a day or so before the test to clear your bowel of any residue
  • drinking clear fluids only the day before the examination
  • taking laxatives to clear your upper bowel
  • an enema to make sure the lower part of the bowel is empty.
  • If you have any questions or the explanation is unclear, please ask your doctor or nurse.

Sigmoidoscopy or colonoscopy

During these investigations the doctor passes a scope (a tube with a small camera on the end) into your bowel. A sigmoidoscopy looks at the lower part of your large bowel, while the colonoscopy looks further up the colon.

The doctor can see if there is part of the lining of the bowel which looks different, for example there may be a polyp (a small smooth growth) or an ulcer.

If the doctor does see something unusual, a biopsy (a sample of tissue) will be taken from this area. The tissue will be sent to the laboratory for examination under the microscope.

Before these examinations you will be given something to make you more relaxed and prevent any discomfort. If you have any questions, please ask your doctor or nurse.

Barium enema

This is an X-ray examination using barium which brightens the X-ray picture. The barium is given as an enema and will outline the lower part of your bowel.

The procedure lasts 15–30 minutes and you should try to hold the contents of the enema for the length of the examination. Afterwards you will be able to empty your bowels. You may be prescribed a mild laxative because barium can cause constipation. Barium can also be very difficult to flush away in the toilet. If you have any questions, please ask your doctor or nurse.

Other tests

You may have other tests, which can include blood tests, abdominal ultrasound, CT scan or MRI scan.

The information from these tests is used to assess the size of the cancer and how far it has spread. This is called ‘staging’. Your doctors need to know the extent of the cancer to help them decide on the most appropriate treatment for you.

Staging of colorectal cancer is based on a physical examination, the results of tests and what the doctors find at the time of surgery.

Colorectal cancer treatment

Treatment will usually be an operation to remove the cancer and/or to relieve your symptoms. You may also have chemotherapy or radiotherapy as well as an operation.

There are several ways of treating colorectal cancer and your treatment will be planned individually for you. Don't be concerned if you talk to other people who are receiving similar, but different, treatments.


An operation may be performed to remove the cancer and part of the bowel on either side of this. Depending on the extent of the operation the two ends of the bowel may be stitched together.

If the tumour is sited low in your rectum, there may not be enough bowel left to join together. In this case you may have to have a colostomy formed. A colostomy, or stoma, is an artificial opening created when the healthy part of your bowel is brought out onto the surface of your abdomen. Your stool will be passed through this opening instead of through your rectum as before. You will need to wear an appliance (bag) to collect your stools. This type of colostomy will be permanent.

In some situations you may need to have a temporary colostomy formed to rest your bowel while healing takes place. This is usually only for a few weeks and will be discussed with you by your doctor.

If it is possible to say before your operation that you will need to have a colostomy, a stoma care nurse will visit you. They will explain exactly what will happen and what to expect. The stoma care nurse will show you how to care for your colostomy and help you adapt to living with a stoma. They can provide support over a long period of time.

If you have any questions or there is anything you don't understand, please speak to your doctor or nurse.


Chemotherapy (drug treatment) may be recommended for you. Chemotherapy means treatment with anti-cancer drugs, which are given to destroy or control cancer cells by damaging them so that they can't divide and grow.


Radiotherapy uses high-energy X-rays to kill cancer cells and is given using a machine similar to an X-ray machine but slightly larger. The treatment area will include the tumour and the surrounding lymph nodes (glands) if necessary. The treatment will planned specifically for you to make sure that the cancer cells are destroyed with the least amount of damage to normal tissues.

Side effects

Your bowel habits may change during radiotherapy, for example you stool may become loose or you may develop diarrhoea. If this happens, please tell your doctor, radiographer or nurse. You will be given advice on diet and medicine can be prescribed to help you. Make sure you drink plenty of fluids.

Your bladder may be included in the treatment field and, if so, you may experience some discomfort when passing urine. You may also want to pass urine more frequently. Once again, make sure you drink plenty of fluids and tell your doctor about this problem.

After treatment for colorectal cancer

Having and being treated for colorectal cancer will have an effect on your life, and there are other things which you should be aware of in addition to the side effects of treatment.


The doctor will ask you to attend hospital at regular intervals during and after your treatment. You will be given an appointment for the outpatients clinic and, as time passes, the appointments will probably become less frequent.

Each time you attend, the doctors will examine you. Blood tests or X-rays may be repeated to check your recovery and make sure the cancer hasn't come back.

Eating and drinking

After treatment for colorectal cancer there are usually no restrictions on what you can eat and drink, including alcohol in moderation. If you would like advice about your diet, please ask to see the dietician.


Colorectal cancer isn't contagious and can't be passed on through physical contact, including sex.

Following surgery or radiotherapy you may need to try different sexual positions until you find one which is comfortable for both of you.

Men who have had an operation to the lower abdomen or radiotherapy to this area may have difficulty in obtaining or maintaining an erection. This can be very distressing. If this is likely to happen in your case, it will be discussed with you before the operation.

Many men, regardless of age, find it embarrassing and difficult to discuss such a personal subject. However, most doctors are very understanding and can offer advice or refer you on to a therapist for help.

Women who have had surgery or radiotherapy may experience vaginal dryness or pain on intercourse. Do speak to your doctor or nurse if you need further advice as there may be simple solutions which can help.

Specialist nurses, for example your stoma care nurse, are always willing to discuss these personal problems with you.


Radiotherapy and chemotherapy may affect your fertility; following these, sperm and eggs may not be formed normally, if at all. This should be discussed with you before treatment. You or your partner should take contraceptive precautions during treatment and for at least one year afterwards. If you have any questions, please ask your doctor or nurse.