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Bowel cancer
Health Guide
What is bowel cancer?

Bowel cancer refers to cancer of the colon (large bowel) or rectum and is often referred to as colorectal cancer . The colon is the last part of the digestive system and is a muscular tube. The rectum is a short tube leading from the colon to the anus and holds faecal mater until ready to be excreted. Bowel cancer begins in the inner lining (mucosa) of the colon or the rectum.

If not treated the tumour becomes bigger and may protrude into the bowel blocking it eventually. Furthermore, the tumour may form an ulcer, which can bleed . As the tumour enlarges it also spreads through the wall of the outer surface of the bowel. Like all malignant cancers, it can spread to other parts of the body to form secondary cancers (eg cancer of the liver)3. This occurs via the blood stream and the lymphatic system. Cancer can also spread to nearby organs such as the bladder .


Bowel cancer is mainly a disease seen in Western Europe, Australia, New Zealand and North America. Every year in New Zealand, approximately 2000 people are diagnosed with bowel cancer. Approximately 1000 people per year also die from bowel cancer . It is in fact the second most common cancer for both men and women4. The incidence of developing Bowel cancer is known to increase with age with over 90% of bowel cancers registered in people over the age of 504.

Cause of disease

What actually cause bowel cancer is uncertain however diet is thought to have a role3,4. Diet with high animal fat and low fibre intake may predispose an individual to develop Bowel cancer. Some foods are also known to have a protective affect. Evidence suggests eating fruits, vegetables breads and cereals may help to prevent bowel cancer4, .

People are also thought to have a greater chance of bowel cancer it they have the following risk factors.

  1. A strong family history of bowel cancer. The New Zealand cancer society defines this as one close relative with bowel cancer particularly if they developed the cancer under the age of 55 years or two close relatives who develop bowel cancer4.
  2. Familial adenomatous polyposis (FAP), which is a rare genetic disease (runs in families). It causes small non-cancerous growths known as benign polyps to develop in the bowel. Over time these may become cancerous4,6.
  3. A inflammatory bowel disease known as ulcerative colitis can also cause cancer in the long term4,6.


Being familiar with the symptoms of bowel cancer is important as with early diagnosis bowel cancer can be treated more effectively However many tumours do not initially produce symptoms or the symptoms (blood loss, constipation) are misinterpreted leading to delayed diagnosis3.

Some of the common symptoms of bowel cancer are listed below11, :

  1. Fresh blood in stool as a result of bleeding in the bowel.
  2. Changes in bowel habits such as constipation or diarrhoea. These changes can be lasting or alter between the two
  3. Recurring pain in the abdomen or rectum
  4. Weight loss
  5. Feeling that the bowel doesn't empty completely and/or a strained feeling in the rectum.

Bowel cancer is often associated with anemia as a result of tumour bleeding7.Where the cancer protrudes into the bowel and causes obstruction, the following symptoms occur7:

  1. Constipation
  2. Vomiting
  3. Fleeing bloated
  4. Griping pains in the abdomen


In those patients without symptoms of bowel cancer screening test with FOBT (faecal occult blood test) may identify early signs of disease4. This test checks for blood in faeces, which can be a sign of bowel cancer. Unfortunately however this test is not always reliable, In two trials half the patients with bowel cancer were missed. Furthermore

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