Genetic counseling in hereditary nonpolyposis colorectal cancer.

Recent identification of gene mutations responsible for hereditary nonpolyposis colorectal cancer (HNPCC) has made possible the presymptomatic diagnosis of at-risk family members. If DNA testing shows that a family member is a gene carrier, that individual's lifetime cancer risk is approximately 90%. If the test is negative, the family member's cancer risk drops to that of the general population. Presymptomatic DNA-based diagnosis consists of pretest counseling, the actual DNA test, and posttest counseling. Pretest counseling focuses on the benefits, limitations, and possible adverse effects of testing, and the advantages and drawbacks of screening methods. Posttest counseling sessions explore the test result, and family members' reactions to it. A multidisciplinary team approach is necessary for the management of HNPCC families.