[Familial colorectal and breast carcinoma--genetic counseling and presymptomatic diagnosis].

Several types of hereditary cancer can be prevented from progressing to advanced stages by regular surveillance of the person at risk and hence by the early treatment of a developing neoplasia. Genetic counselling of such patients and their relatives is therefore an important task whose value often remains unrecognized. This is especially true for the common forms of hereditary cancer such as breast and colorectal cancer, which aggregate in up to 5% of all patients according to the rules of autosomal-dominant inheritance. Preventive measures are particularly promising in the case of familial cancer because persons at risk are motivated to seek medical help. Genetic counselling is a multifaceted process and involves more than an accurate diagnosis and risk estimate. The counseled patient expects and deserves an open and reasonable answer to his questions about the implications of his/her cancer predisposition or his family history. Accurate diagnosis of the underlying susceptibility is the cornerstone of genetic counselling because most cancers seem to have multiple causes. Different genes located on different chromosomes can independently give rise to the same malignancy. Besides heterogeneity, presymptomatic testing for inherited susceptibilities to cancer raises many issues including therapy, access, intense anxiety, and discrimination.