[Genetic testing when tumor susceptibility, especially for colorectal cancer, is suspected]

Approximately 5-10% of all tumours can be explained by inherited susceptibilities. While some of the underlying traits are rare, the total number of subjects at an increased genetic tumour risk is quite large in our population. Genetic testing has gained considerable importance in the identification of persons with such traits allowing their systematic medical surveillance and early detection and treatment of tumours. Predisposition for tumour development has to be considered in the following cases, 1) when the onset of the neoplasm was at an age earlier than the average of that for the general population, 2) if synchronous or metachronous foci occur in the same organ or organs at an increased risk due to the same trait, 3) if the tumour displays typical histological pecularities or occurs at an unusual position within an organ, 4) if the patient suffers from a genetic disorder with an increased tumour risk, 5) if several relatives were/are suffering from the same or genetically associated tumours and/or 6) a "tumour gene" has already been identified in a relative by molecular genetic testing. Thanks to the progress of the genome project, the number of genes identified has led to a steady increase in the detection of mutations which may lead to tumourigenesis. Identification and characterisation of a mutated "tumour gene" in a patient allows the verification of a clinical and/or genealogical diagnosis. Genetic testing is indicated if medical non-heroic measures are available to identify a tumour at an early state and to prevent its progression to an incurable disease. Also, healthy relatives can profit from the identification and characterization of the tumour trait. If they have inherited the same gene mutation they also need a systematic medical surveillance to improve their life expectancy and quality. Because gene testing raises a broad spectrum of medical, social, psychological, and ethical issues, genetic counselling has to be offered before, during and after molecular genetic analysis. In particular in genetic counselling related to tumour risks, problems often develop due to the involvement of an unusually large number of experts representing various medical disciplines who may hold different views. If several professionals are involved in the diagnosis and the genetic workup it is advisable for them to communicate directly with each other and not to misuse the patient as their "go-between". In this paper special emphasis is given to genetic testing for predispositions to colorectal cancer.