[Report of Chinese Children's Cancer Group acute lymphoblastic leukemia 2015 multicenter study]

Objective: To evaluate the outcomes and identify the prognostic factors of childhood acute lymphoblastic leukemia (ALL) treated with Chinese Children's Cancer Group study ALL-2015 (CCCG-ALL-2015) protocol. Methods: There were two randomization studies in CCCG-ALL-2015 study. A total of 7 640 newly diagnosed ALL patients in 20 hospitals of multi-institutional study group between January 2015 and December 2019 were treated with unified protocol. CCCG-ALL-2015 protocol featured risk-directed therapy based on morphology, immunophenotype, and genetic features, and adjusted according to minimal residual disease (MRD) assay on day 19 and day 46 of induction, which totally omitted prophylactic cranial irradiation. Two randomized controlled trails were designed. Children with Philadelphia chromosome-positive ALL (Ph⁺ALL) were randomly treated with dasatinib (Ph-D group) or imatinib (Ph-I group). During the latter half of continuation therapy, children were randomly treated with seven pulses of vincristine plus dexamethasone (group A) or not (group B). The survival rates of different groups were compared. Event-free survival (EFS) and overall survival (OS) curves were estimated according to the Kaplan-Meier method and compared by Log-rank test. Cox proportional hazards model was used for multivariate analysis. Results: Of the 7 640 enrolled patients, there were 4 521 males and 3 119 females, 7 508 (98.3%) entered complete remission. The 5-year EFS was 60.1% (95%CI 49.8%-72.5%) in the Ph-D group and 39.4% (95%CI 26.9%-57.7%) in the Ph-I group (χ²=5.00, P=0.020). Between patients with lower risk (LR) and intermediate and higher risk (I/HR) treated with (group A) or without (group B) additional pulse of vincristine plus dexamethasone, there were no difference in 5-year EFS and OS. The one-sided 95% upper confidence bound for the difference in 5-year EFS and OS were 0.02 and 0.01 for LR, 0.05 and 0.01 for I/HR, establishing non-inferiority, lower than 0.05. The follow-up time was 3.5 (2.4,4.8) years. The 5-year OS was 90.9% (95%CI 90.2%-91.7%), and EFS was 80.1% (95%CI 79.0%-81.2%). The 5-year cumulative risk of any relapse was 15.3% (95%CI 14.3%-16.3%).The cumulative risk of isolated central nervous system (CNS) relapse was 1.9% (95%CI 1.6%-2.2%), and any CNS relapse 2.7% (95%CI 2.3%-3.1%). The 5-year cumulative risk of death during remission was 1.3% (95%CI 1.0%-1.6%). In the multivariate analysis, the independent factors associated with inferior EFS of patients with B-ALL were age≥10 years, male sex, white blood cell count ≥50×10⁹/L, CNS2 or CNS3 status, BCR-ABL fusion, KMT2A rearrangements, without ETV6-RUNX1 fusion and the presence of MRD>0.01% at day 19 or 46 (all P<0.05). Among patients with T-ALL, the significant predictors for lower EFS were the BCR-ABL1 fusion and MRD≥0.10% at day 46 (both P<0.05). Conclusions: Patients treated with CCCG-ALL-2015 protocol without the use of prophylactic cranial irradiation have favorable outcomes, and the cumulative risk of isolated CNS relapse and cumulative risk of death during remission are low. Intensive chemotherapy including dasatinib yield superior results compared to imatinib in the treatment of Ph⁺ALL. Vincristine plus dexamethasone pulses can be omitted for ALL children without decrease in treatment ontcome during the latter half of continuation therapy.