Recognition of cancer susceptibility in children with cancer is of high clinical significance. It may require modifications in treatment protocols to prevent toxicities or the risk of second malignancies, and cancer surveillance for early detection of malignancies in the child and his or her family members. Unfortunately, in many children in whom a cancer predisposing syndrome (CPS) is suspected, the underlying genetic cause cannot be found. In this study I will use a range of genomic techniques to identify underlying genetic causes in children with cancer with a high suspicion of a cancer predisposing syndrome. These children will be included based on additional features as a family history of cancer, congenital features or other physical signs, or secondary primary malignancies. With this information we expect to identify novel cancer predisposing genes and mechanisms.