Increased survival rate by the pediatric acute lymphoblastic leukemia therapy intensification based on minimal residual disease levels along with protocol-based risk classification by early response.

Purpose Minimal residual disease (MRD)-guided therapy is a global standard for pediatric acute lymphoblastic leukemia (ALL). We assessed the impact of MRD-driven intensification alongside protocol-defined risk groups. Methods This retrospective analysis included 209 patients with ALL (January 2013–June 2023). MRD was assessed using 6- to 8-color flow cytometry at the end of each phase before the maintenance phase. Post-induction treatment was determined by early response, National Cancer Institute risk, and cytogenetics. High-risk (HR) patients followed the Korean HR or CCG-1882 protocols; standard-risk (SR) patients followed a modified COG-AALL0331 protocol. Treatment was intensified if flow-MRD ≥ 0.1% was identified. Results Overall, 103 and 106 patients were classified as SR and HR, respectively. The 5-year overall survival (OS) and event-free survival (EFS) were 92.5% and 84.3% in all patients, respectively. Thirty SR and 18 HR patients received intensified chemotherapy. Treatment intensification significantly improved EFS in patients with high MRD (94.2% vs 75.5%, p = 0.04), particularly marked in post-induction MRD-high patients (90.0% vs 19.0%, p = 0.035). The survival difference between RER and SER groups was eliminated after MRD-based intensification. The implementation rates of treatment intensification varied over time (9.1% before 2015, 28.6% in 2016–2019, 13.9% in 2020–2023), reflecting improved risk stratification and therapy selection. Conclusion MRD-guided therapy intensification markedly improved survival outcomes in pediatric ALL when combined with risk-based protocols, highlighting the importance of MRD monitoring for optimizing risk-adapted treatment strategies.