Asparaginase is used in the treatment of childhood lymphoblastic leukemia. Approximately 1/3 of the patients develops blocking antibodies against native E.coli asparaginase during the second exposure, so that they do not benefit from treatment and thus may have a worse prognosis.~PEG-asparaginase is less immunogenic so that fewer patients may develop antibodies during the second exposure.~There is no published study about the antibody formation after treatment of children with PEG-asparaginase during two treatment courses.~The first part of the study is a description of the pharmacokinetics of PEG-asparaginase after intramuscular administration in order to determine the correct dose.~The second part of the study is a comparison of antibody formation during two treatment courses after intramuscular administration og native E.coli asparaginase and PEG-asparaginase.~Other side effects than antibodies will be registered during treatment with PEG-asparaginase. Finally comparison of the 5-year EFS between the groups (native E.coli asparaginase and PEG-asparaginase as well as patients who have and have not developed antibodies) will be evaluated.
The purpose of this study is~to determine the correct dose for intramuscular administration~to compare the frequency of antibody formation after intramuscular administration of native E.coli asparaginase and PEG-asparaginase during two treatment courses in the treatment of childhood lymphoblastic leukemia