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Colorectal cancer risk estimates based on family history typically include only close relatives.
Dr David Taylor and colleagues from the USA reported familial relative risk in probands with various combinations, or constellations, of affected relatives, extending to third-degree.
The team used a population-based resource that includes a computerized genealogy linked to statewide cancer records to identify genetic relationships among colorectal cancer cases, and their first-, second-, and third-degree relatives.
Familial relative risks were estimated by comparing the observed number of affected persons with a particular family history constellation to the expected number, based on cohort-specific colorectal cancer rates.
The researchers found a total of 2,327,327 persons included in 3 generation family histories were analyzed, and 10,556 had a diagnosis of colorectal cancer.
 | | The familial relative risk for persons with affected relatives was 1.9 | | Gastroenterology |
The familial relative risk for colorectal cancer in persons with affected relatives was consistent with published estimates.
In the absence of a positive first-degree family history, only 1 constellation had an familial relative risk estimate that was significant.
The familial relative risk for persons with affected relatives was 1.9, increasing to familial relative risk 3.3 for probands with 1 to 3 affected first- and second-degree relatives, and more than 3 affected third-degree relatives.
Dr Taylor's team concluded, “Increased numbers of affected first-,degree relatives influences risk much more than affected, second-,degree relatives or third-degree relatives.”
“However, when combined with a positive first-degree family history, a positive second- and third-degree family history can significantly increase risk.”
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