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The purpose of the Southern Cross Medical Library is to provide information of a general nature to help you better understand certain medical conditions. Always seek specific medical advice for treatment appropriate to you. This information is not intended to relate specifically to insurance or healthcare services provided by Southern Cross. For more articles go to the Medical Library index page.

Bowel (colorectal) cancer - symptoms, treatment

Bowel cancer is a cancer that affects the digestive system between the stomach and the anus. It can affect either the small bowel where our food is digested, or the large bowel (colon and rectum) where what remains of our food is turned into solid waste and expelled from the body. This page deals primarily with cancer of the large bowel (also known as colon or colorectal cancer) which is more common than small bowel cancer.

Characteristic symptoms of colorectal cancer include changes in bowel habits and bleeding from the rectum. Treatment involves surgery, followed in some cases by chemotherapy or radiation therapy. In many cases, colorectal cancer is curable if detected sufficiently early in the course of the disease.

About the bowel and colorectal cancer

Bowel cancer, along with prostate cancer, is one of the most commonly diagnosed cancers among New Zealand adults with around 3000 new cases per year.  New Zealand has one of the highest rates of bowel cancer and deaths from bowel cancer in the western world.

The bowel is a 6-metre-long tube of muscle that is part of the digestive system (gastrointestinal tract) extending from the stomach to the rectum and anus.

gastrointestinal tract

The stomach breaks down food and liquid, which is then passed into the small bowel to be digested. From there, nutrients are absorbed into the blood stream while the remains pass into the large bowel, which is made up of two parts - the colon and the rectum. The 1.5 metre-long colon removes liquid from digested food and turns it into solid waste. The 12 to 15 centimetre-long rectum holds this solid waste until it is expelled through the anus as a bowel motion (also referred to as stools or faeces).

The most common form of bowel cancer occurs in the colon and rectum, which make up the large bowel. Hence, it is also referred to as colon cancer or colorectal cancer. Cancer of the small bowel is uncommon.

Colorectal cancer is an abnormal growth of cells lining the walls of the colon or rectum, and can be associated with polyps, which begin as non-cancerous (benign) fleshy growths that develop on the wall of the bowel. Polyps become more common as people age. The abnormal cell growth results in the formation of a malignant lump or tumour, which can affect bowel function.

Colorectal cancer usually occurs after the age of 50 years.


It is not known what causes bowel / colorectal cancer, but several risk factors that appear to increase the likelihood of developing the disease have been identified.

A family history of bowel cancer or polyps – having a first-degree relative (father, mother, brother, sister) or second-degree (grandfather, grandmother, aunt, uncle) relative with bowel cancer or polyps – is a risk factor for bowel cancer.

The risk of developing the condition is also increased in people with an inflammatory bowel disease, primarily long term ulcerative colitis but also some instances of Crohn's disease.

Diets high in fat are believed to be a factor in the development of bowel cancer – countries with high rates of bowel cancer have a higher consumption of fat than countries with low bowel cancer rates. It is thought that digestion of fat in the colon results in the formation of cancer-causing chemicals (carcinogens). Consuming less fat should help to reduce exposure to these fat-derived carcinogens.

Signs and symptoms

Signs and symptoms of colorectal cancer are many and varied, including:

  • Blood in the stools and/or bleeding from the rectum
  • A change in bowel habit lasting longer than 6 weeks (e.g. loose stools, diarrhoea or constipation)
  • Stomach pain (often severe)
  • Lumps or a mass in the abdomen
  • Weight loss
  • Weakness and tiredness (symptoms of anaemia).


A diagnosis of colorectal cancer is made by a combination of tests including a digital rectal examination (where your doctor will feel for suspicious lumps using a gloved finger), testing for blood in the stools (faecal occult blood test), blood tests for iron-deficiency anaemia, and x-rays of the digestive tract.

The definitive test for colorectal cancer is a colonoscopy. A colonoscopy is performed by a colorectal surgeon or gastroenterologist using a colonoscope (a thin, flexible, tubular instrument with a video camera at one end) to view the lining of the intestines and, if necessary, to take biopsy tissue samples for laboratory testing.

Staging of colorectal cancer

When colorectal cancer is diagnosed, additional tests (including MRI, Ct and PET scans) are performed to determine the extent of the disease, which is a process called staging. The staging for colorectal cancer is as follows:

  • Stage I (least advanced cancer) – cancer involving only the innermost layers of the colon or rectum wall. The likelihood of cure for stage I cancer is over 90%, emphasizing the importance of early detection of the cancer
  • Stage II – cancer exhibiting greater growth and extension of tumour through the wall of the colon or rectum into adjacent structures.
  • Stage III – cancer involving spread of the cancer to local lymph nodes (metastasis).
  • Stage IV (most advanced cancer) – cancer having spread to distant organs, usually the liver and lungs, or lymph nodes far from the original tumour. 


The primary treatments for colorectal cancer are surgery to remove cancer cells, and chemotherapy and radiation therapy to kill cancer cells.

For most people with stage I and stage II colorectal cancer, surgery alone is the only treatment required. However, once the cancer has spread to local lymph nodes (stage III), the risk of the cancer returning remains high even if all visible evidence of the cancer has been removed by the surgery. In this case, chemotherapy is likely to be used to lower the risk of the cancer returning.

There are several different options for chemotherapy for the treatment of colorectal cancer. The simplest treatments involve a single type of chemotherapy drug, given either by pill or by injection into a vein, but sometimes a combination of chemotherapy drugs is recommended. Chemotherapy is typically given for a total of 6 months.

Once colorectal cancer has spread to other parts of the body (stage III and IV cancer), chemotherapy is the best treatment, and although not curative it can extend life expectancy and quality of life.

Biological drugs, known as monoclonal antibodies (e.g. cetuximab), are newer medicines that can be used in combination with chemotherapy in cases of metastatic bowel cancer. By binding to specific growth-stimulating proteins on the surface of the cancer cells monoclonal antibodies block the growth of the cancer cells.
Radiation therapy is usually used for cancer of the rectum, since tumours in the rectum are often more difficult to remove surgically than are tumours in other parts of the bowels.


The specific cause of bowel cancers is not known but lifestyle factors may contribute to its development. Therefore, making the following lifestyle changes, or modifications, may lower the risk of developing bowel cancers:

  • Maintaining a healthy body weight
  • Being physically active
  • Eating a diet rich in whole grains, cereals, fruit and vegetables
  • Reducing intake of fats, salt and sugars
  • Drinking alcohol in moderation
  • Stopping smoking.

Further information

The Cancer Society of New Zealand operates a phone service staffed by specialist nurses to support patients diagnosed with cancer, including bowel / colorectal cancer, as well as their friends and families.

Cancer Society of New Zealand
PO Box 12700
Wellington 6144
Freephone: 0800 CANCER (226 237)

Beat Bowel Cancer Aotearoa is a nationwide patient-led organisation that aims to reduce the impact of bowel cancer on the community by raising awareness and providing education and support services for bowel cancer patients and their families.

Beat Bowel Cancer New Zealand.
PO Box 6405
Dunedin North 9059


Dragovich, T. (2017). Colon cancer (Web Page). Medscape Drugs and Diseases. New York, NY: WebMD LLC. [Accessed: 01/12/17]
Jackson, C., et al. (2014). Rectal cancer: future directions and priorities for treatment, research and policy in New Zealand. N Z Med J. 2014;127(1395):63–72.
Ministry of Health (2016). Cancer: New registrations and deaths 2013 (Report). Wellington: New Zealand Ministry of Health.
New Zealand Guidelines Group (2012). Bowel cancer (Booklet). Wellington: New Zealand Ministry of Health.
NHS Choices (2016). Dehydration (Web Page). Redditch: National Health Service (NHS)
England. [Accessed: 01/12/17]
O’Toole, M.T. (Ed.) (2013). Colorectal cancer. Mosby’s Dictionary of Medicine, Nursing & Health Professions (9th ed.). St Louis, MI: Elsevier Mosby.

Last updated December 2017

Go to our Medical Library Index Page to find information on other medical conditions.