ASPG and acute lymphoblastic leukemia: Systemic etoposide54 and 6-mercaptopurine55 can also reach adequate concentrations in CSF, as well as systemic administration of L-asparaginase can result in prolonged CSF depletion of L-asparagine.56 In childhood ALL, delivery of Erwinia-derived asparaginase was associated with CNS relapse at a nearly six times rate than patients treated with Escherichia coli-derived asparaginase.57 The experience with the use of systemic chemotherapy indicates that, when given alone, it is not sufficient for CNS prophylaxis.