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Family history – relative(s) with bowel cancer

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

However, for around 30% of all bowel cancer cases diagnosed there is a family history, hereditary contribution or a combination of both.

Generally speaking, the more members of the family affected by bowel cancer, and the younger they were at diagnosis, the greater the chance of a family link.

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.

Non-modifiable risk factors

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

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What is my bowel cancer risk?

Average risk of bowel cancer

  • No bowel cancer symptoms
  • No hereditary conditions
  • No personal health history of
    • bowel cancer; or
    • special types of polyps called adenomas; or
    • inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease.
  • No family history of bowel cancer (no first-degree or second-degree relatives)

Please note: a first-degree relative can be a parent, brother, sister or child. A second-degree relative can be an aunt, uncle, grandparent, grandchild, niece, nephew, or half-brother or half-sister.

Near or above average risk of bowel cancer

Family history of bowel cancer

  • Only one first-degree relative with bowel cancer diagnosed at age 60 years or older – above average, but less than twice the average risk 
  • No family history of bowel cancer (no first-degree or second-degree relatives) – near-average risk

Please note: a first-degree relative can be a parent, brother, sister or child. A second-degree relative can be an aunt, uncle, grandparent, grandchild, niece, nephew, or half-brother or half-sister.

Moderately increased risk of bowel cancer

Personal health history

Family history of bowel cancer

  • Only one first-degree relative diagnosed with bowel cancer before age 60 years; or
  • One first-degree relative AND one or more second-degree relatives with bowel cancer diagnosed at any age; or
  • Two first-degree relatives with bowel cancer diagnosed at any age.

Your risk of developing bowel cancer is at least 2 times higher than average, but could be up to 4 times higher than average.

Please note: a first-degree relative can be a parent, brother, sister or child. A second-degree relative can be an aunt, uncle, grandparent, grandchild, niece, nephew, or half-brother or half-sister.

Potentially high risk of bowel cancer

Hereditary conditions

Significant family history of bowel cancer

  • Two first-degree relatives AND one second-degree relative with bowel cancer, with at least one diagnosed before age 50; or
  • Two first-degree relatives AND two or more second-degree relatives with bowel cancer diagnosed at any age; or, with at least one diagnosed before age 55 years; or
  • Three or more first-degree relatives diagnosed with bowel cancer at any age.

Your risk of developing bowel cancer is at least 4 times higher than average, but could be up to 20 times higher than average.

Please note: a first-degree relative can be a parent, brother, sister or child. A second-degree relative can be an aunt, uncle, grandparent, grandchild, niece, nephew, or half-brother or half-sister.