Age and health history can affect the risk of developing bowel cancer.

Anything that increases your chance of developing bowel cancer is called a cancer risk factor. Some risk factors can be avoided, but many cannot.

Age, family history, hereditary conditions and personal health history can all influence your bowel cancer risk. These factors cannot be changed and are therefore referred to as ‘non-modifiable’.

Around 30% of all bowel cancer cases diagnosed are due to a hereditary contribution, family history, or a combination of both. The other 70% of people have no family history of the disease and no hereditary contribution.

Non-modifiable bowel cancer risk factors, for both men and women include:

  • Age – bowel cancer risk increases with age. Incidence begins to increase significantly between the ages of 40 and 50, and age-specific incidence rates increase in each succeeding decade thereafter (i.e. 50-60; 60-70; 70-80 etc). Although bowel cancer is less common among younger adults, rates are on the rise, with 1-in-9 bowel cancer cases now diagnosed in Australians under age 50.
  • A family history of bowel cancer
  • A personal history of cancer of the colon, rectum, ovary, endometrium, or breast
  • A history of polyps in the colon
  • A history of ulcerative colitis (ulcers in the lining of the large intestine) or Crohn’s disease
  • Hereditary conditions, such as Familial Adenomatous Polyposis (FAP) and Hereditary Non-Polyposis Colon Cancer (HNPCC; Lynch Syndrome).

There is emerging evidence regarding type 2 diabetes (usually non-insulin dependent) as a potential risk factor for bowel cancer.

Having one or more risk factors does not always mean that you will get bowel cancer, and some people who are diagnosed with bowel cancer may not have any known risk factors.

Age

The risk of bowel cancer increases with age.

As people age, they are more likely to grow polyps, some of which may undergo gene changes that turn normal tissue into cancer.

This is why age is considered a non-modifiable bowel cancer risk factor.

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Family history

About 70% of people who develop bowel cancer have no family history of the disease.

Genetic mutations have been identified as the cause of inherited cancer risk in some bowel cancer–prone families; these mutations are estimated to account for only 5% to 10% of bowel cancer cases overall.

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Genetic mutations

The three most common inherited syndromes linked with bowel cancers are:

  • Hereditary Non-Polyposis Colorectal Cancer (HNPCC) (also known as Lynch Syndrome)
  • Familial adenomatous polyposis (FAP)
  • MYH-Associated Polyposis (MAP)
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Inflammatory Bowel Disease (IBD)

Both Crohn’s disease and ulcerative colitis (also known as colitis) are known as inflammatory bowel disease.

Both these conditions can cause inflammation of the bowel (colon and rectum), with similar symptoms and treatments.

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Non-modifiable risk factors

A Bowel Cancer Australia resource outlining non-modifiable risk factors for bowel cancer, including a family medical history chart.