Abstract: Background: Minimal residual disease (MRD) is used to monitor and assess the treatment response in pediatric acute lymphoblastic leukemia (ALL) and to stratify risk based on MRD levels. Objective: To investigate the prognostic value of regularly monitoring MRD during and after chemotherapy in predicting relapse in children with ALL. Design: Retrospective cohort study Methods: The clinical data of 224 ALL children received CCCG-ALL2015 chemotherapy from January 2015 to February 2020 were retrospectively included in our study. MRD was detected using flow cytometry to analyze the association between regular monitoring of MRD and prediction of recurrence. Main outcome measures: Recurrence free survival (RFS) Results: A total of 224 children were included in this analysis, with 134 males and 90 females, and a median age of 4.8 years. On day 19 (D19) of induction remission, 104 cases (46.4%) were MRD-positive, and on day 46 (D46), 23 cases (10.3%) were MRD-positive. From post-induction remission (week 16) to the end of chemotherapy (week 125), 145 cases remained MRD-negative. During follow-up after the end of chemotherapy (weeks 152-287), 13 cases became MRD-positive, of which 11 (84.6%) relapsed. A total of 28 children relapsed, with a median relapse time of 33 months. Among them, 14 survived, 12 died, and 2 were lost to follow-up. There were 20 cases of bone marrow relapse, including 2 with concurrent testicular relapse and 1 with CNSL and 8 with CNSL alone. The median follow-up time for the 224 children was 52 months (IQR: 36.5-69.5 months), and the 5-year RFS was (84.5±2.8)%. There were statistically significant differences in the 5-year RFS between children with D46 MRD ≥0.01% and <0.01%, as well as between those who remained MRD-negative throughout chemotherapy and those who were MRD-positive at least once (P<0.05). Conclusion: Children with D46 MRD ≥0.01% and those who were MRD-positive at least once during chemotherapy had a poorer prognosis. Regular MRD monitoring during chemotherapy is crucial.

Key words: Children, Acute lymphoblastic leukemia, Minimal residual disease, Recurrence