Genetic Counseling and Testing in Families With Hereditary Nonpolyposis Colorectal Cancer

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Abstract
HEREDITARY nonpolyposis colorectal cancer (also known as HNPCC and Lynch syndrome) is the most common hereditary form of colon cancer. It is estimated to account for between 1% and 5% of the individuals who develop colon cancer.1 It has been estimated that the prevalence of HNPCC mutation carriers among the general population in Western countries is 1 in 740.2 This means that in the United States approximately 380 000 individuals carry an HNPCC mutation and have a greater than 90% lifetime risk of developing one of the cancers associated with HNPCC.3 Some evidence suggests that the risk of colon cancer may vary between men and women.4 In addition to colon cancer, individuals with HNPCC are at increased risk (compared with the general population) for developing cancers of the uterus, small intestine, stomach, urinary tract, kidney, ovary, and other sites.5-7 Lifetime estimates for developing a cancer associated with HNPCC approach 85% for colorectal cancer8 and 40% to 60% for uterine cancer9 (by age 70 years). Risks for cancer of the small intestine, stomach, urinary tract, kidney, ovary, and brain are also elevated but lower compared with the risks for colon and uterine cancer. Accurate and age-related risks for these cancers are not yet available.10