Screening for Colon Cancer in a Relative
If your relative has one first-degree family member (parent, sibling, or child) diagnosed with colon cancer before age 60, they should undergo colonoscopy starting at age 40 or 10 years before the youngest affected relative's diagnosis age (whichever comes first), and repeat every 5 years. 1, 2, 3
Risk Stratification Based on Family History
The screening approach depends critically on the age at diagnosis of the affected family member and the number of affected relatives:
High-Risk Scenarios Requiring Intensive Surveillance
One first-degree relative diagnosed before age 60: Begin colonoscopy at age 40 or 10 years before the affected relative's diagnosis age, whichever is earlier, and repeat every 5 years. 1, 3
Two or more first-degree relatives with colon cancer at any age: Begin colonoscopy at age 40 or 10 years before the youngest affected relative's diagnosis, and repeat every 5 years. This carries a 3-4 times higher risk than the general population. 1, 4, 3
One first-degree relative diagnosed before age 45: This represents the highest empiric risk category (relative risk 3.7-7.18), warranting colonoscopy every 5 years starting at age 35-40. 5
Moderate-Risk Scenarios
- One first-degree relative diagnosed at age 60 or older: Begin average-risk screening at age 40 (not age 45-50) using colonoscopy every 10 years or annual fecal immunochemical test (FIT). The risk is only modestly elevated (1.8-fold) but occurs approximately 10 years earlier than average-risk individuals. 1, 2, 3
When to Consider Genetic Testing
Multiple relatives with colon cancer across generations, especially if diagnosed young: Refer for genetic counseling to evaluate for Lynch syndrome (hereditary nonpolyposis colorectal cancer) or familial adenomatous polyposis. 5, 4
Lynch syndrome confirmed: Colonoscopy every 1-2 years starting at age 25 or 10 years before the youngest affected relative's diagnosis. 5, 1, 4
Familial adenomatous polyposis: Flexible sigmoidoscopy every 2 years starting at age 12-14 for classical FAP, or colonoscopy every 2 years starting at age 18-20 for attenuated FAP. 6, 4
Screening Method Selection
Colonoscopy is strongly preferred over other screening methods for individuals with family history because it allows complete visualization of the entire colon and simultaneous removal of polyps. 5, 1
Approximately 48% of adenomas in first-degree relatives are located beyond the reach of flexible sigmoidoscopy (versus 25% in average-risk individuals), making full colonoscopy essential. 7
Annual FIT is an acceptable alternative only if colonoscopy is declined, but it has lower sensitivity for detecting advanced adenomas. 1, 3
Critical Pitfalls to Avoid
Verify the diagnosis and age of the affected relative: Family history information is often incomplete or inaccurate. Attempt to confirm the diagnosis through medical records when possible. 1
Don't overlook proximal colon lesions: A substantial proportion of lesions in high-risk individuals are restricted to the proximal colon, making sigmoidoscopy inadequate. 5
Reassess if multiple distant relatives are affected: Even if formal criteria aren't met, multiple affected relatives across generations should prompt genetic counseling referral as they may represent unrecognized hereditary syndromes. 5
Don't forget residual risk: Even individuals who don't meet high-risk criteria still have population-level risk and should participate in standard screening programs. 5