Does having a second-degree relative with colon cancer, instead of a first-degree relative, change the recommendation for a colonoscopy given my history of Hodgkin's lymphoma and radiation therapy at 22 years old?

Yes, Having a Second-Degree Relative (Grandparent) Instead of a First-Degree Relative Significantly Changes the Recommendation

You should follow average-risk screening guidelines starting at age 45, not the more intensive surveillance recommended for first-degree relatives. Your history of Hodgkin's lymphoma with radiation therapy at age 22 is the dominant risk factor that should guide your colonoscopy timing, not your grandparent's colon cancer.

Risk Stratification Based on Degree of Relationship

• Second-degree relatives (grandparents, aunts, uncles) with colorectal cancer do not warrant enhanced screening beyond average-risk protocols 1
• The 2003 Gastroenterology guidelines explicitly state that people with one second-degree relative with colorectal cancer should be screened as average-risk persons 1
• Only first-degree relatives (parents, siblings, children) with colon cancer—particularly those diagnosed before age 60—confer sufficient risk elevation to justify more intensive surveillance 1, 2

Your Radiation History Takes Priority

• Your prior radiation therapy to the abdomen/pelvis for Hodgkin's lymphoma at age 22 is a far more significant risk factor than a second-degree family history 1
• Radiation-associated colorectal cancer risk typically begins 10-15 years post-exposure, meaning you should already be in active surveillance
• This radiation history alone warrants colonoscopy screening independent of any family history considerations

Specific Screening Algorithm for Your Situation

• Begin colonoscopy screening now (or at age 32, which is 10 years post-radiation), repeating every 5 years based on your radiation exposure 1
• Your grandparent's colon cancer does not modify this recommendation—it would only matter if it were a parent, sibling, or child diagnosed before age 60 1, 2
• If your radiation field did not include the abdomen/pelvis, then follow average-risk screening starting at age 45 with colonoscopy every 10 years 2

Why Second-Degree Relatives Don't Change Recommendations

• Research shows that having only second-degree relatives affected yields a polyp detection rate of approximately 43%, which is essentially identical to those with first-degree relatives (46%), except when multiple first-degree relatives are affected (67%) 3
• The absolute risk increase from second-degree relatives is insufficient to justify the cost, risk, and resource utilization of enhanced screening 1
• Guidelines consistently distinguish between first-degree and second-degree relatives, with only the former warranting earlier or more frequent screening 1, 2, 4

Critical Caveat About Your Radiation History

• Verify the exact radiation field from your Hodgkin's treatment records—if it included abdominal/pelvic nodes or extended below the diaphragm, you need colonoscopy surveillance regardless of family history 1
• Mantle field radiation (chest/neck only) would not increase colorectal cancer risk, but any subdiaphragmatic radiation absolutely does
• This radiation risk supersedes all family history considerations for second-degree relatives 1