Background: Due to the long-term sequelae of cranial radiotherapy (CRT), contemporary treatment protocols for children with acute lymphoblastic leukemia (ALL) aim to limit the use of prophylactic CRT. For patients with central nervous system (CNS) involvement with ALL at diagnosis, the use of CRT remains common. Children \u3c5 years of age are a particularly challenging subgroup in whom the consequences of CRT can be devastating. Procedure: This study retrospectively describes the overall (OS) and event-free survival (EFS) of young children (1-5 years) who were treated for CNS-positive ALL at the Hospital for Sick Children between 2000 and 2013. Results: Of a total of 19 patients, two were treated with upfront CRT, both as part of the conditioning regimen prior to HSCT. All patients received intensification of CNS-directed chemotherapy by triple intra-thecal chemotherapy (84.2%), use of dexamethasone in induction (57.9%) and maintenance (66.7%), and high-dose methotrexate (77.8%). The OS was 84.2±8.4% and EFS was 79.0±9.4% with a median follow-up time of 4.3 years (range, 2.6-8.2). The cumulative incidence of CNS relapse was 5.2±5.1%. Conclusions: We conclude that omission of CRT from the treatment of young children with ALL involving the CNS is associated with acceptable survival and avoids potentially devastating late effects in this group
