PURPOSE

Minimal residual disease (MRD)-guided therapy is the global standard treatment for pediatric acute lymphoblastic leukemia (ALL). We assessed the impact of MRD-driven intensification along with protocol-defined risk groups in pediatric ALL treatment.

METHODS

This retrospective analysis included 209 patients with ALL (treated between January 2013 to June 2023). MRD was assessed using six- to eight-color flow cytometry at the end of each phase before the maintenance phase. Post-induction treatment was determined based on early response, National Cancer Institute risk, and cytogenetics. High-risk (HR) patients followed the Korean HR or CCG-1882 protocols and standard-risk (SR) patients followed the modified COG-AALL0331 protocol. Treatment was intensified if flow-MRD ≥ 0.1% was identified.

RESULTS

Overall, 103 and 106 patients were classified as having SR and HR, respectively. The 5-year overall survival (OS) and event-free survival (EFS) were 92.5% and 84.3%, 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 in post-induction patients with high MRD (90.0% vs. 19.0%, p = 0.035). The difference in survival between rapid early responder (RER) and slow early responder (SER) groups was eliminated after MRD-based intensification. The implementation rates of treatment intensification varied over time (9.1% before 2015, 28.6% during 2016-2019, and 13.9% during 2020-2023), reflecting improved risk stratification and therapy selection.

CONCLUSION

MRD-guided therapy intensification markedly improved survival outcomes in patients with pediatric ALL when combined with risk-based protocols, highlighting the importance of MRD monitoring for optimizing risk-adapted treatment strategies.