Bowel cancer – risk factors

The cause of bowel cancer is still unknown; however research has identified a number of factors that increase the risk of developing bowel cancer.

People who are at increased risk of developing bowel cancer are strongly advised to contact their doctor to discuss regular surveillance options.


Everyone is at risk of developing bowel cancer, and the risk of developing bowel cancer increases with age.

Previous history

Polyps are small growths on the inner lining of the bowel or rectum that are quite common. About 1 in 4 people will have had a polyp by the age of 50, and 1 in 2 people will have had them by age 70.

People with a history of polyps in the bowel, especially those who have had multiple polyps, have a higher risk of developing bowel cancer.

People who have previously recovered from bowel cancer may develop the disease again in other parts of the bowel. If the person was younger than 50 years of age when the bowel cancer was originally diagnosed the risk of developing a subsequent cancer becomes even greater.

Chronic inflammatory bowel disease

There are two types of chronic inflammatory bowel disease: ulcerative colitis and Crohn’s disease.

These are conditions in which the bowel becomes inflamed due to injury, infection or irritation. If this inflammation occurs for long periods of time it causes damage to the lining of the bowel.

This damage increases the chances of bowel cancer developing. The risk of developing bowel cancer depends on how badly inflamed the bowel is and how long the inflammation occurs for.

Family history

A person’s risk of bowel cancer may be increased if one or more of their close relatives have been diagnosed with bowel cancer. However, only 15 per cent to 20 per cent of people with bowel cancer have a history of the disease within their family.

Two inherited conditions that can increase bowel cancer risk are:

  • Familial Adenomtous Polyposis (FAP)
  • Hereditary Non-Polyposis Colorectal Cancer (HNPCC).

Both are very uncommon conditions but can significantly increase the risk of bowel cancer for those who are affected.

Familial Adenomatous Polyposis (FAP)

FAP accounts for less than 1 per cent of all bowel cancers. FAP is caused by a change in a particular region of our DNA, called the APC gene. DNA contains all the information our cells need to make an identical copy of themselves.

The change in the APC gene causes multiple polyps to grow in the bowel and these polyps can turn into cancer if left untreated. The polyps commonly start growing during the late teens or early twenties, but may occur at any age. FAP is passed down in families. If a parent has the altered APC gene there is a 50 per cent chance a child may also have it.

Hereditary Non-Polyposis Colorectal Cancer (HNPCC)

HNPCC accounts for about 1 to 4 per cent of bowel cancers. HNPCC, also known as Lynch syndrome, is also caused by an altered gene. HNPCC is characterised by no or very few polyps, which makes the condition hard to diagnose. People with HNPCC often have bowel cancers that develop when they are in their 30s or 40s.

Type 2 diabetes and increased insulin levels

Type 2 diabetes, or non-insulin-dependent diabetes, is a condition in which the body can no longer respond to the hormone insulin. This results in high levels of insulin in the blood, known as hyperinsulinemia.

High levels of insulin lead to increased levels of a protein called insulin-like growth factor-1 (IGF-1) in the blood. IGF-1 is a protein that is believed to help cancer cells grow.

People with type 2 diabetes often have the disease long before it is diagnosed and treated. As a result, their bodies are exposed to high levels of IGF-1 for a long time. People with type 2 diabetes also put on weight (body fat). These 2 factors therefore increase the chances of people with type 2 diabetes developing bowel cancer.

Where to get help

More information

More information on bowel cancer is available from Cancer Council Western Australia (external site).

This information provided by
Logo: Cancer Council Western Australia

Cancer Council Western Australia

This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

Bowel cancer screening program