At what age should I have my first colon cancer screening if a relative is diagnosed with colon cancer and has a genetic mutation associated with the disease?

Screening Recommendations for Relatives of Patients with Genetic Colon Cancer Mutations

When Your Relative Has a Confirmed Genetic Mutation

If your relative tested positive for Lynch syndrome (HNPCC), you should begin colonoscopy at age 20-25 years or 10 years younger than the earliest case in your family, whichever comes first, and repeat every 1-2 years. 1

If your relative tested positive for familial adenomatous polyposis (FAP), you should begin annual sigmoidoscopy at age 10-12 years. 1

Lynch Syndrome (HNPCC) Screening Protocol

• Start colonoscopy at age 20-25 years or 10 years before the youngest affected relative's diagnosis age, whichever is earlier 1
• Repeat colonoscopy every 1-2 years (not every 5-10 years like other family history scenarios) 1
• Pursue genetic counseling and testing to determine if you carry the mutation 2
• If you test positive for Lynch syndrome, continue every 1-2 year colonoscopy surveillance indefinitely 2
• If you test negative for the family mutation, you can follow average-risk screening guidelines 1

Familial Adenomatous Polyposis (FAP) Screening Protocol

• Begin annual sigmoidoscopy at age 10-12 years to detect polyp development early 1
• Genetic testing should be performed after genetic counseling, ideally starting at age 10 years 1
• If the family mutation is identified and you test negative, you are at average risk 1
• If you test positive or sigmoidoscopy shows polyps, colectomy is typically required given the near 100% cancer risk 1

Attenuated APC (AAPC) Variant

• Use colonoscopy instead of sigmoidoscopy because polyps tend to occur in the right colon 1
• Begin screening in the late teens or early 20s depending on family polyp expression patterns 1
• This variant typically presents with 20-100 adenomas rather than hundreds 1

Critical Distinction: Genetic Testing Status Matters

The screening approach differs dramatically based on whether your relative has a confirmed hereditary syndrome versus simply having colon cancer:

• Confirmed Lynch syndrome or FAP: Follow the aggressive protocols above starting in childhood/young adulthood 1
• Family history without identified genetic syndrome: Begin colonoscopy at age 40 or 10 years before the relative's diagnosis age, whichever is earlier, repeating every 5 years 2, 3, 4

If Your Relative Was "Tested for the Gene" But Results Are Unknown

You should clarify whether your relative tested positive for a hereditary cancer syndrome. 1 If testing was negative or no mutation was found (which occurs in ~20% of FAP families), you would follow family history-based screening rather than hereditary syndrome protocols 1. The distinction between these two pathways is critical—one begins screening in childhood/adolescence with frequent intervals, while the other begins at age 40 with less frequent surveillance.

Common Pitfalls to Avoid

• Don't assume all colon cancer is hereditary: Only about 5-10% of colon cancer cases are due to identifiable genetic syndromes like Lynch syndrome or FAP 1
• Verify the genetic test results: Family members often misunderstand whether testing was done, what was tested, or what the results showed 2
• Don't delay genetic counseling: If a hereditary syndrome is confirmed in your family, you need formal genetic counseling before testing to understand implications and avoid discrimination risks 1
• Sigmoidoscopy is insufficient for AAPC: This variant requires full colonoscopy due to right-sided polyp predominance 1

Type of Relative Matters

The screening recommendations above apply primarily to first-degree relatives (parents, siblings, children) of affected individuals 1, 2. Second-degree relatives (grandparents, aunts, uncles) with hereditary syndromes may also warrant genetic counseling, but the urgency and intensity differ based on inheritance patterns 1.