At what age should a patient with a first-degree relative (parent, sibling, or child) who had colon cancer start colon cancer screening?

Colon Cancer Screening When a First-Degree Relative Had Colon Cancer

Begin colonoscopy screening at age 40 or 10 years before the age your relative was diagnosed with colon cancer, whichever comes first. 1, 2

Screening Algorithm Based on Relative's Age at Diagnosis

If Your Relative Was Diagnosed BEFORE Age 60

Colonoscopy every 5 years starting at age 40 or 10 years before their diagnosis age, whichever is earlier. 1, 2, 3

• This applies whether you have one first-degree relative diagnosed before age 60, or two or more first-degree relatives diagnosed at any age 1, 2
• The risk is 3-4 fold increased when diagnosed before age 60, with the highest risk (3.8-fold) when diagnosed before age 45 1, 4
• For example, if your parent was diagnosed at age 52, you should start colonoscopy at age 40 (not age 42), and repeat every 5 years 2

If Your Relative Was Diagnosed AT OR AFTER Age 60

Begin screening at age 40 using average-risk options: colonoscopy every 10 years OR annual FIT. 1, 2, 4

• When diagnosed at ≥60 years, the risk is only 1.8-fold increased, which is substantially lower than earlier diagnosis 1, 4
• You follow average-risk screening intervals but start 10 years earlier than the general population 1, 4
• Colonoscopy remains the preferred method even in this scenario because it allows complete visualization and polyp removal in one procedure 2

Critical Distinctions That Change Your Screening Plan

Multiple Affected Relatives

If you have TWO or more first-degree relatives with colon cancer at any age, use the more intensive protocol: colonoscopy every 5 years starting at age 40 or 10 years before the youngest diagnosis. 1, 2

• This applies regardless of the ages at which your relatives were diagnosed 2
• The risk increases to 4.2-fold with multiple affected relatives 1

Advanced Adenoma in a Relative

If your first-degree relative had a documented advanced adenoma (≥1 cm, villous features, or high-grade dysplasia) diagnosed before age 60, screen as if they had colon cancer diagnosed before age 60. 1, 2

• This means colonoscopy every 5 years starting at age 40 or 10 years before their diagnosis 1, 2
• Documentation is critical—if you cannot verify the adenoma was advanced, assume it was not and follow average-risk screening 1

Why Colonoscopy Is Strongly Preferred Over Other Tests

Colonoscopy is the preferred screening method for all individuals with family history because it allows complete visualization and simultaneous polyp removal. 2, 3

• FIT is an acceptable alternative only if you decline colonoscopy, but it has lower sensitivity for advanced adenomas and requires consistent annual adherence 2
• Other tests like CT colonography or flexible sigmoidoscopy are second-tier options with significant disadvantages 3

When to Consider Stopping Screening

Consider stopping screening at age 75 if you are up to date with screening and have had negative tests, particularly colonoscopy, or when life expectancy is less than 10 years. 2, 5, 3

• If you have never been screened, screening may be considered up to age 85 depending on your age and comorbidities 5, 3
• Screening is not recommended after age 85 5

Common Pitfalls to Avoid

Do not wait until age 45 or 50 to begin screening if you have any first-degree relative with colon cancer—screening must begin at age 40 at the latest. 2

Do not use 10-year colonoscopy intervals if your relative was diagnosed before age 60 or if you have two or more affected first-degree relatives—these situations require 5-year intervals. 2

Verify the exact age at diagnosis and whether it was truly colon cancer versus an advanced adenoma, as this critically determines your screening intensity. 2

• Family history information is often incomplete or inaccurate, and attempts should be made to verify the diagnosis whenever possible 1, 2

When to Suspect Hereditary Syndromes

If you have multiple relatives with colon cancer or polyps across generations, especially with diagnosis before age 50, seek genetic counseling for possible Lynch syndrome or familial adenomatous polyposis. 2, 5

• Lynch syndrome requires colonoscopy every 1-2 years starting 10 years before the youngest affected relative's diagnosis 2
• Familial adenomatous polyposis requires annual flexible sigmoidoscopy beginning at age 10-12 5, 6

Evidence Quality Note

The recommendation to begin screening at age 40 in persons with an affected first-degree relative is based on the observation that colon cancer incidence in this group parallels average-risk individuals but occurs approximately 10 years earlier. 1, 4 While mortality reduction studies specifically for this population are limited, the gradient of risk based on age at diagnosis and number of affected relatives is well-established from large meta-analyses. 1