Numerous inherited genetic changes predisposing to cancer have already been
identified and the number is increasing. Accurate prediction of individual
risk by means of molecular diagnosis implies clinical consequences in the
treatment of cancer-predisposing syndromes. Using familial adenomatous poly
posis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC) as an ex
ample, we present here the underlying genetic changes that contribute to tu
mor development. These genetic alterations can be efficiently identified th
rough molecular diagnostic techniques. Identification of the familial germl
ine mutation permits one to distinguish mutation carriers from non-mutation
carriers within affected families and results in individually tailored sur
veillance and prevention. Therefore, molecular diagnosis is making a contri
bution to the advances in preventive surgical therapy. The indications are
discussed.