Screening for Colorectal Cancer

Colorectal (bowel) cancer is common in Australia, with about 14,800 new cases each year and a lifetime risk of approximately 1 in 23 by age 85. Screening detects occult bleeding from cancers and precancerous lesions before symptoms develop.

  1. Average-risk screening
    • iFOBT every 2 years from age 45–74 years.
    • Age 45–49: eligible for the National Bowel Cancer Screening Program (NBCSP), but must request the first free kit or obtain one through their healthcare provider.
    • Age 50–74: kits are automatically mailed every 2 years.
    • After completing a kit, subsequent kits are automatically sent every 2 years until age 74.
    • Colonoscopy is not recommended as routine screening for average-risk asymptomatic people.
  2. iFOBT
    • Detects small amounts of blood in stool that may arise from colorectal cancer or adenomas.
    • Negative iFOBT does not exclude bowel cancer.
    • Positive iFOBT → diagnostic assessment, usually colonoscopy.
    • Do not use screening iFOBT to investigate symptoms.
  3. Family history – Category 1: average or slightly increased risk
    • No family history, or
    • 1 first-degree relative diagnosed at ≥60 years.
    • Screening remains iFOBT every 2 years from 45–74 years.
    • Family history at this level does not justify screening colonoscopy.
  4. Family history – Category 2: moderately increased risk
    • 1 first-degree relative diagnosed <60 years, or
    • 1 first-degree + ≥1 second-degree relative diagnosed at any age, or
    • 2 first-degree relatives diagnosed at any age.
    • Risk is approximately 2–4 times average.
    • Colonoscopy every 5 years from:
      • 10 years younger than the earliest diagnosis in a first-degree relative, or
      • age 50,
      • whichever is earlier.
    • Continue to age 74.
  5. Family history – Category 3: potentially high risk
    • Where Lynch syndrome has been excluded:
      • 2 first-degree + 1 second-degree relative, with ≥1 diagnosed <50 years, or
      • 2 first-degree + ≥2 second-degree relatives diagnosed at any age, or
      • ≥3 first-degree relatives diagnosed at any age.
    • Risk is approximately 4–20 times average.
    • Colonoscopy every 5 years from:
      • 10 years younger than the earliest diagnosis in a first-degree relative, or
      • age 40,
      • whichever is earlier.
    • Continue to age 74.
    • Consider referral to a familial cancer / clinical genetics service.
    • For expanded detail: Genetic Counselling
  6. Hereditary colorectal cancer syndromes
    • Lynch syndrome, familial adenomatous polyposis (FAP) and MUTYH-associated polyposis (MAP) require syndrome-specific surveillance.
    • Do not apply the generic Category 3 schedule to a known hereditary cancer syndrome.
    • Refer for genetics/familial cancer assessment where the pedigree suggests inherited cancer susceptibility.
    • Particularly consider referral with:
      • colorectal cancer <50 years
      • multiple Lynch-associated cancers in one person
      • multiple affected close relatives
      • colorectal and endometrial cancers within the family.
    • For expanded detail: Genetic Counselling
  7. Previous colorectal cancer, adenomas or inflammatory bowel disease
    • These patients require surveillance, not population screening.
    • Surveillance intervals depend on previous cancer, polyp findings and underlying disease.
    • Long-standing ulcerative colitis and Crohn colitis increase colorectal cancer risk.
    • For expanded detail: Follow-up Post Colorectal Cancer
  8. Symptoms are not screening
    • Rectal bleeding
    • persistent change in bowel habit
    • unexplained iron deficiency anaemia
    • unexplained weight loss
    • abdominal or rectal mass.
    • These require diagnostic investigation regardless of age or previous screening results.
    • DRE is not a population screening test, but may be appropriate when investigating symptoms.
  9. Aspirin
    • For people at higher-than-average colorectal cancer risk, consider aspirin 100 mg daily from age 45–70 years after discussing benefits and bleeding risk.
    • The previous advice of 100–300 mg from age 50–70 for ≥2.5 years is no longer the clean current Red Book recommendation.
  10. What does a positive iFOBT mean?
    • In 2024, approximately 5.8% of NBCSP screening tests were positive.
    • Among people with a recorded diagnostic assessment after a positive result:
      • about 1 in 29 had confirmed or suspected bowel cancer
      • about 1 in 3 had an adenoma.
    • Therefore, most positive iFOBTs are not cancer, but the probability of important colorectal pathology is high enough that follow-up is essential.
  11. Risk reduction
    • Eat plenty of vegetables, fruit and whole grains.
    • Minimise red meat, processed meat and heavily grilled/barbecued meat.
    • Maintain a healthy weight.
    • Exercise regularly.
    • Limit alcohol.
    • Do not smoke.

The useful exam skeleton

  • Average risk → iFOBT q2y age 45–74
  • Positive iFOBT → colonoscopy
  • 1 FDR ≥60 → iFOBT
  • 1 FDR <60 / 2 FDR → Category 2 → colonoscopy q5y from 50 or 10 years before
  • Heavy family history → Category 3 → colonoscopy q5y from 40 or 10 years before
  • Lynch / FAP / MAP → specialist genetic pathway
  • Symptoms → investigate, don’t screen

Current Key Resources