Relative risk of colorectal cancer decreases with age among individuals with a family history of colorectal cancer. 

However, no screening recommendations specify less frequent screening with increasing age. 

Dr Steffie Naber and colleagues from the Netherlands determined whether such a refinement would be cost effective.

The researchers determined the relative risk for colorectal cancer for individuals based on age and number of affected first-degree relatives (FDRs) using data from publications. 

For each number of affected FDRs, the team used the Microsimulation Screening Analysis model to estimate costs and effects of colonoscopy screening strategies with different age ranges and intervals. 

Screening was then optimized sequentially, starting with the youngest age group, and allowing the interval of screening to change at certain ages. 

Strategies with an incremental cost effectiveness ratio below $100,000 per quality-adjusted life year were considered cost effective.

For people with 1 affected FDR, the team found that screening every 3 years beginning at an age of 40 years is most cost effective. 

If no adenomas are found, the researchers noted that screening interval can gradually be extended to 5 and 7 years, at ages 45 and 55 years, respectively. 

From a cost-effectiveness perspective, individuals with more affected FDRs should start screening earlier and at shorter intervals. However, frequency can be reduced if no abnormalities are found.

Dr Naber's team concludes, "Using a microsimulation model, we found that for individuals with a family history of colorectal cancer, it is cost effective to gradually increase the screening interval if several subsequent screening colonoscopies have negative results and no new cases of colorectal cancer are found in family members."