Families at risk for colorectal cancer: risk assessment and genetic testing.

As befits a common cancer, a family history of colorectal cancer (CRC) is reported by about 10% of individuals. The discovery of the genetic basis of hereditary nonpolyposis CRC and familial adenomatous polyposis has opened up the possibility for determining genetic predisposition to CRC in asymptomatic family members of affected cases. This article reviews the information needed for accurate risk assessment for those with a family history of CRC. Screening recommendations and the current status of genetic testing, including review of available tests such as microsatellite instability, immunohistochemistry for hMSH2 and hMLH1, testing for I1307K, and gene testing for germline mutations in hMSH2 and hMLH1 are discussed. At the current time, reliable, informative genetic testing, capable of application to broad segments of the population, is an unrealized goal. But as the methodology for testing improves and as better appreciation of the significance and meaning of a positive or negative test result ensues conditions for increased use of genetic testing could emerge.