Pegylated-asparaginase (PEG-ASP) is an important part of the treatment of childhood acute lymphoblastic leukaemia (ALL). Unfortunately 13% of patients develops allergy and further treatment is impossible. Furthermore, 6% of patients have developed antibodies (silent inactivation) and have no effect of the PEG-ASP treatment. Truncated asparaginase therapy is associated with inferior event-free survival outcomes, in particular relapse in central nervous system (CNS).