ASSESSMENT OF MINIMAL RESIDUAL DISEASE BY NEXT-GENERATION FLOW CYTOMETRY AFTER INITIAL INDUCTION THERAPY FOR ACUTE MYELOID LEUKEMIA IN A PUBLIC PEDIATRIC HOSPITAL

Abstract

Introduction: Measurable residual disease (MRD) has been reported as a strong independent prognostic factor in AML, particularly in guiding decisions for hematopoietic cell transplantation in first remission. The recent consensus guidelines established by the European Leukemia NET (ELN) have emphasized molecular characterization and risk stratification for individuals with AML and recommended MRD by flow cytometry (FC) assessment in the evaluation of treatment response and monitoring in AML. Aim: We evaluated the impact of MRD status on clinical outcomes after initial induction therapy in pediatric patients diagnosed with AML and MRD-FC as a tool to support relapse risk classification. Material and methods: Overall, 48 bone marrow (BM) samples of 16 pediatric patients (62% F and 38% M), median age of 8,5 years – 0 to 16 years) were diagnosed with AML between 2021-2024, at a public pediatric hospital. All patients received the chemotherapy protocol GELMAI. BM samples were obtained at different time points after treatment (15 post induction I, 14 post induction II, 13 post intensification, 2 pre-transplant and 4 post-transplants). MRD-FC was performed in all samples with a panel with antibody combinations - 8 colors, according to ELN. All BM samples were studied with the acquisition of ≥1,5 × 106 events per sample. FACS Canto cytometer and Infinicyt software were used for acquisition and analysis. Risk classification considers molecular and cytogenetics findings at diagnosis and MRD status during treatment response assessment (positive MRD > 0.1% after induction II). The patients were classified according to GELMAI protocol as low-risk, intermediate risk, and high-risk. Event-free survival curves (EFS), defined as the time from diagnosis to progression and/or disease recurrence or patient death during the study. The study was approved by local ethics committee. Results: Positive MRD was detected in 42% (20/48) of BM studied, being 67% (10/15) at post induction I, 35% (5/14) at post induction II and 38% (5/13) at post intensification. In this study, 56% of patients were stratified as high-risk. Throughout the study, 3/16 patients relapsed after intensification phase and 4/16 died early (one after induction phase and one before starting treatment). Negative MRD AML patients at post-induction II had longer EFS compared to positive MRD cases and did not relapse, although the difference was not statistically significant (p = 0.06). Discussion: AML is a complex hematological neoplasm from a cytogenetic, molecular and morphological point of view. Several studies have shown MRD by flow cytometry is an important biomarker in AML being used for prognostic, predictive, monitoring, and efficacy-response assessments. MRD is a fast, sensitive method and can provide an independent prognostic factor when evaluated after post-induction therapy. We demonstrated that MRD is crucial for risk stratification and treatment planning, with MRD positivity linked to an increased risk of early relapse, though not statistically significant due to limited sample size and follow-up. Thus, further investigations with larger series of paired diagnostic and follow-up BM samples from AML patients are required. Conclusion: MRD-FC has become an indispensable tool for prognosis, clinical management, and guiding decisions, being feasible to introduce as a tool for treatment response assessment and risk stratification after post-induction.