A colorectal cancer simulation

How it works

The simulation follows 1,000 people year by year across a lifetime, showing how many develop colorectal cancer and how many die of it without screening. It then shows the screened counterfactual for the same people.

This is a year-by-year Monte Carlo simulation: each person gets an individual cancer risk and timing, then the model follows the cohort through later adulthood.

The baseline risk. Without screening, the lifetime chance of colorectal cancer is about 8%. This is the midpoint of the no-screening range in the USPSTF’s CISNET modeling. We do not use the familiar “1 in 25” figure, because the screening that many people get is baked into that number, and we are simulating a no-screening baseline.

Screening prevents cancers outright, reducing cancer incidence by about 60%. In the lifetime model, the death benefit emerges from both prevented cancers and cancers caught earlier: overall, screening reduces colorectal cancer deaths by about 74%.

Caveats. We depict the average risk profile here. People with a family history may face significantly higher risk than the simulation shows. Some forms of screening also entail their own risks, not depicted here.