Lymphoblastic Lymphoma, Childhood

Primary objectives: * Randomization R1, all patients eligible: To examine, whether the cumulative incidence of relapses with involvement of the CNS (CNS relapse, pCICR) can be decreased by a modified induction therapy including dexamethasone (experimental arm) instead of prednisone (standard arm) * Randomization R2, only patients with high risk LBL eligible: to examine, whether the probability of event-free survival (pEFS) in these patients can be improved by receiving an intensified treatment arm versus a standard treatment arm (as used in the EURO-LB 02)