·A retrospective study was conducted on the cases with treatment failure in 330 children who were initially diagnosed as having ALL in Shanghai Children's Hospital from January 2006 to June 2017 to analyze the reasons for failure. The clinical characteristics of the children with different reasons were analyzed respectively. Kaplan-Meier survival curve analysis and COX regression model were used to explore the recurrence rate, overall survival (OS) rate and risk factors of recurrence. The difference of the stages of infection occurrence in the children with different risk levels was explored by χ² test.

·Among the 330 children with ALL, 84 cases failed in treatment. The reasons for treatment failure included disease recurrence (58 cases), death due to severe infection (19 cases), second tumor occurrence (2 cases), and death from other causes (5 cases). Totally 58 ALL children relapsed, whose median recurrence time was 27 (2-95) months. The 5-year cumulative recurrence rate was (18.2 ± 2.3)%, and the 10-year cumulative recurrence rate was (22.4 ± 2.9)%. Multivariate analysis showed that poor treatment response in the early stage (HR=5.43, P=0.000) and medium and high risk of disease (HR=2.26, P=0.017) were independent risk factors for recurrence. According to the recurrence time, the 5-year OS rate of children with very early recurrence was (16.7±10.2)%, significantly lower than that of children with early and late recurrence (P=0.000). According to the location of recurrence, the 5-year OS rate of children with simple bone marrow recurrence was (42.0±10.2)%, significantly lower than that of children with simple extramedullary recurrence (P=0.044). Of the 55 children with severe infection, 26 cases had sepsis, 20 cases had respiratory infection with acute respiratory distress syndrome, and 9 cases had severe intestinal infection. There were statistically significant differences in the stage distribution of infection occurrence in the children with different risk levels (P=0.019). Low-risk children were more likely to have serious infection during the induction and consolidation treatment phase (P=0.022), and medium-and-high-risk children were more likely to have serious infection in the mid-stage of intensive treatment (P=0.044).

·Recurrence and death from infection are the main causes for treatment failure in childhood ALL. Active prevention and treatment of very early recurrence and infection can reduce the incidence of treatment failure and improve the long-term survival rate of the children.