AbstractBackgroundThe survival of children with acute lymphoblastic leukemia (ALL) has improved due to changes in the treatment and the disease diagnosis. A significant advance was the incorporation of asparaginase. However, hypersensitivity reactions are a common cause of early discontinuation of this drug.AimThe proposed study aims to evaluate early interruptions and the influence of the number of asparaginase doses effectively administered on the prognosis of patients with ALL.Methods and ResultsAn observational cohort study was carried out, with retrospective data collection, in medical records. The prognostic variables indicated in the protocol applied were used, and the principal outcomes were 5 years event‐free survival (EFS) and 5 years of overall survival (OS) probability. Statistical analyzes were performed using SPPS 20.0 and R. In Cox's proportional hazards model for EFS and OS, variables of prognostic importance (n = 126 children) were: high‐risk group (HGR), by the protocol classification, and less than 10 doses of asparaginase. The increased risk of events and death in HGR, who did less than 10 doses, was 3.6 and 7 times, respectively. The study did not show statistical significance for the number of asparaginase doses in patients who were not at high risk.ConclusionsWe demonstrated that the early interruption of asparaginase treatment could negatively impact the prognosis of patients with ALL, especially HGR, reinforcing the need for careful diagnosis of reactions and the availability of alternative types of asparaginase.