This article was last reviewed on
This article waslast modified on 28 January 2018.
What is it?

The bowel forms part of the digestive system and is divided into two parts, the small bowel and the large bowel. The large bowel is made up of the colon and rectum; the colon makes up most of the 5 foot length of the large bowel.

Food passes from the stomach to the small bowel. After the small bowel takes nutrients into the body, any undigested food passes through the large bowel, where water is removed from the waste matter.

Bowel cancer is also known as colon, rectal or colorectal cancer. Bowel cancer is the third most common cancer in the UK, after lung and breast cancer. It is the second most common cause of cancer death, after lung cancer. Approximately 95% of all diagnoses are in people over the age of 50. Most cases of bowel cancer begin with the development of benign polyps, finger-like growths that protrude into the intestinal cavity. These benign polyps are not cancer and relatively common in people over age 50. They can become cancerous, though, with the ability to invade the normal bowel and spread to other parts of the body (metastasize). The tumours can create blockages in the intestine, preventing elimination.

The exact causes of bowel cancer are not known, but risk appears to be associated with genetic, dietary, and lifestyle factors. Those with a personal or family history of bowel cancer or polyps are at a higher risk, as are those with ulcerative colitis, inflammatory bowel disease, and immunodeficiency disorders. A very rare inherited disease, called Familial Adenomatous Polyposis (FAP), causes benign polyps to develop early in life and cancer develops in almost all affected persons unless the colon is removed. Another genetic condition called Hereditary Non-polyposis Colorectal Cancer (HNPCC) accounts for around 2-5% of cases of bowel cancer. Polyps develop at a younger age and at a greater frequency than in individuals who do not have the disease, but not in such large numbers as FAP.

The risk of bowel cancer increases with age and with the occurrence of cancers in other parts of the body. High fat and high meat diets are risk factors, especially when combined with minimal fruit, vegetable, and fibre intake. Lifestyle risk factors include cigarette smoking, obesity, and a sedentary lifestyle.

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About Bowel Cancer
  • Symptoms

    Bowel cancer frequently develops without early symptoms. Symptoms that can occur include:

    • Diarrhoea, constipation, or other changes in bowel habit lasting 10 days or more
    • Bright red blood or mucus in the stool
    • Very dark flecks in the stool (which can also be due to blood)
    • Unexplained anaemia
    • Abdominal pain and tenderness in the lower abdomen
    • Abdominal discomfort (frequent gas pains, bloating, fullness, and cramps)
    • A feeling of still wanting to go to the toilet even after having emptied the bowels
    • Complete blockage of the intestine
    • Weight loss for no known reason
    • Constant tiredness

    Although these symptoms can be caused by cancer they are also seen in a number of other conditions. It is important to talk to your doctor so the cause can be established. Polyps may develop into a cancer but if they are detected and removed bowel cancer can often be prevented. If bowel cancer is detected early, it is up to 90% curable.

  • Tests

    Deciding which screening test to use and how often ultimately depends on a person's individual risk of bowel cancer. If a first-degree relative has had bowel cancer, for instance, screening should start 10 years prior to the age that relative was diagnosed to help identify possible pre-cancerous polyps.

    The NHS Bowel Cancer Screening Programme now offers screening every two years to all men and women aged 60 to 74 in England using a guaiac based faecal occult blood test (gFOBT). People within the age range are automatically sent an invitation, then their screening kit, so they can perform the test at home. After the first screening test, individuals are sent an invitation and screening kit every two years. The gFOBT does not diagnose bowel cancer, but the results will indicate whether an individual may need an examination of their bowel by colonoscopy.
    For further information about the NHS Bowel Cancer Screening Programme see www.cancerscreening.nhs.uk/bowel/index.html. Separate screening programmes are offered in Wales, Scotland and Northern Ireland.

    There are four common screening tests for detecting bowel cancer:

    • Faecal occult blood (FOB) test is a test for hidden blood in the stool.
    • Sigmoidoscopy is an examination of the rectum and lower colon with a rigid or flexible lighted instrument. 
    • Double barium contrast enema is a series of X-rays of the colon and rectum. The patient is given an enema with a white, chalky solution that outlines the colon and rectum on the X-rays.
    • Colonoscopy is an examination of the rectum and entire colon with a lighted instrument. It may be the most useful, but it is also the most invasive.

    There is also a newer test called CT colonography or virtual colonoscopy. Instead of having a colonoscope put inside the bowel, it may be possible to have an examination with pictures created by a computer. Air or carbon dioxide is pumped into the back passage to help open up the bowel. Two CT scans are performed; one when the patient is lying on their back and one lying on their front. A computer matches up the two scans and makes a 'virtual' scan of the inside of the bowel.

    In addition to these, a doctor may perform a rectal examination to feel for a rectal mass with a gloved finger. Most bowel cancers, however, are beyond the reach of a finger and have no symptoms; hidden blood in the stool, detected as FOB, is often the first and only warning sign.

    Individuals in families that are affected by FAP or HNPCC will have a genetic test are used to determine whether they have inherited the disease This information will be used to decide how frequently they are tested by colonoscopy.

  • Treatments

    If a doctor finds what may be bowel cancer he or she will perform a biopsy, removing some tissue for examination under a microscope by a pathologist. If the tissue is cancerous, the doctor will want to learn the stage (or extent) of disease. Treatment will depend in part on the stage of the bowel cancer; it is categorised by how far it has spread from its original site.  Many doctors in the UK now use the TNM stages or the number stages of bowel cancer.  These stages are used across the world and are taking over from the Dukes' staging system.

    TNM staging of bowel cancer

    TNM stands for tumour, node, metastases. This staging system can describe the size of a primary tumour (T), whether any lymph nodes contain cancer cells (N) and whether the cancer has spread to another part of the body (M).

    Number staging of bowel cancer:

    • Stage 0: Very early cancer of the innermost lining of the bowel
    • Stage 1: Tumour in the inner layers of the colon
    • Stage 2: Tumour in the outer layers of the colon and/or nearby tissue
    • Stage 3: Tumour has spread to lymph nodes
    • Stage 4: Tumour has spread to distant organs

    There are more details about staging on the Cancer Research UK web site

    All stages of bowel cancer are usually treated by surgically removing the cancer and possibly some of the surrounding tissue. For Stages 2 and 3, chemotherapy and/or radiation therapy may be added to help kill the cancer and shrink the tumour. Chemotherapy and radiation may also be used in Stage 4 to improve symptoms and to prolong life.