Bowel cancer causes and symptoms


The exact cause of bowel cancer is not known. However, some factors increase the chance of developing bowel cancer, including:

  • Getting older – bowel cancer more commonly affects people aged 50 and over.
  • Bowel diseases – people who have an inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis, have a significantly increased risk.
  • Lifestyle factors – being overweight, doing little physical activity, a diet high in fat or animal products, alcohol consumption and smoking can play a part.
  • Strong family history – bowel cancer can run in the family. Whether you’re at increased risk depends on who was diagnosed and at what age.
  • Inheriting a rare genetic disorder – See next page for more information about familial adenomatous polyposis and hereditary non-polyposis colorectal cancer.

Polyps in the colon are a risk factor for bowel cancer. If polyps are removed, the risk of bowel cancer is reduced.

Family history of cancer

If one or more of your family members (such as a parent or sibling) have been diagnosed with bowel cancer before the age of 55, it may run in your family. This is also a possibility if two relatives on the same side of your family have bowel cancer.

If you are concerned about bowel cancer because of your family history, see your general practitioner (GP) for regular checkups and discuss whether genetic testing would be suitable for you. Doing regular physical activity, maintaining a healthy weight and eating a diet high in fruit, vegetables and fibre may help protect against bowel cancer.

Inherited genetic conditions

There are two very rare conditions that can run in families. About 5% to 6% of bowel cancers are caused by these inherited genetic conditions.

Familial adenomatous polyposis (FAP)

This condition causes many polyps to form in the bowel. If polyps caused by FAP are not removed, they usually become cancerous.

Hereditary non-polyposis colorectal cancer (HNPCC)

This increases the risk of developing bowel cancer and other cancers. Not everyone with HNPCC will develop bowel cancer.


In its early stages, bowel cancer often has no noticeable symptoms. Symptoms some people experience include:

  • a change in bowel habits such as appearance of stools, constipation, or smaller, more frequent bowel movements
  • a feeling of fullness in the bowel or rectum
  • a feeling that the bowel hasn’t emptied completely after a bowel movement
  • blood in the stool or on the toilet paper
  • unexplained weight loss
  • weakness or fatigue
  • rectal or anal pain
  • feeling very tired or breathless (anaemia).

Cancer of the bowel may cause a blockage (bowel obstruction). This causes symptoms such as abdominal pain, feeling bloated, constipation and being sick.

Many of the symptoms of bowel cancer are common to other large bowel conditions, such as haemorrhoids or tears in anal tissue. Some foods or medications can also change bowel habits or cause stools to turn red or black. If you have any of the above symptoms, talk to your doctor.

Last Reviewed: 01 February 2011
Reproduced with the kind permission of The Cancer Council New South Wales.
©Copyright: myDr, Cirrus Media Pty Ltd, 2000-2016. All rights reserved.


  • Cancer Council NSW. February 2011. Understanding Bowel Cancer. A guide for people with cancer, their families and friends. (accessed Jan 2013.)