Impact of colon cancer screening on family history phenotype.

Background: If effective cancer screening is more common in people with a family history of cancer, the relationship between family history and cancer incidence may become distorted.

Methods: To assess the impact of screening on the association between colorectal cancer family history and risk of colorectal cancer, we developed a model to simulate screening patterns in those with and without a family history.

Results: The introduction of screening reduces the apparent risk of colorectal cancer associated with family history in subsequent generations. This reduction becomes more pronounced as the difference in the uptake of screening between those with a family history and those without becomes larger.

Conclusion: A result of effective screening is that observed family history of colorectal cancer may no longer match inherited risk, and observed family history may fail to be a strong risk factor. This may have implications for exposure-disease relationships if screening is differentially associated with the exposure.