1.1 To identify key adverse events developing in patients (cases) with a primary cancer diagnosed at age 21 or younger. 1.2 To characterize the key adverse events with respect to the nature of the primary malignancy (pathology, stage) and coded details of the therapeutic protocol. 1.3 To identify treatment-related and demographic risk factors through a direct comparison of the case-group and controls identified from the remaining patients with the same primary diagnosis. 1.4 To compare the frequency of mutations or polymorphisms in specific candidate genes in cases and controls, using constitutional DNA and RNA from the cases and controls. 1.5 To explore the role and nature of gene-environment interaction in the development of key adverse events.