Comparison of treatment strategies in de novo pediatric acute lymphoblastic leukemia (ALL) requires standardized measures of efficacy. Key parameters that define disease-related events, including complete remission (CR), treatment failure (TF; not achieving CR), and relapse (loss of CR) require an updated consensus incorporating modern diagnostics. We collected the definitions of CR, TF, and relapse from recent and current pediatric clinical trials for the treatment of ALL, including the key components of response evaluation (timing, anatomic sites, detection methods, and thresholds) and found significant heterogeneity, most notably in the definition of TF. Representatives of the major international ALL clinical trial groups convened to establish consensus definitions. CR should be defined at a time point no earlier than at the end of induction and should include the reduction of blasts below a specific threshold in bone marrow and extramedullary sites, incorporating minimal residual disease (MRD) techniques for marrow evaluations. TF should be defined as failure to achieve CR by a prespecified time point in therapy. Relapse can only be defined in patients who have achieved CR and must include a specific threshold of leukemic cells in the bone marrow confirmed by MRD, the detection of central nervous system leukemia, or documentation of extramedullary disease. Definitions of TF and relapse should harmonize with eligibility criteria for clinical trials in relapsed/refractory ALL. These consensus definitions will enhance the ability to compare outcomes across pediatric ALL trials and facilitate development of future international collaborative trials.

Childhood Cancer Research Unit Karolinska Institutet Astrid Lindgren's Children's Hospital Karolinska University Hospital Stockholm Sweden

Children's Cancer Research Institute St Anna Children's Hospital Department of Pediatrics Medical University of Vienna Vienna Austria

Chilean National Pediatric Oncology Group Santiago Chile

Clinic of Pediatric Hematology and Oncology University Medical Center Hamburg Eppendorf Hamburg Germany

Department of Oncology St Jude Children's Research Hospital Memphis TN

Department of Pediatric Hematology and Oncology Institute of Pediatrics Faculty of Medicine University of Debrecen Debrecen Hungary

Department of Pediatric Hematology and Oncology Istituto di Ricovero e Cura a Carattere Scientifico Ospedale Pediatrico Bambino Gesù Sapienza Università di Roma Rome Italy

Department of Pediatric Oncology Dana Farber Cancer Institute Boston MA

Department of Pediatrics and Adolescent Medicine University Hospital Rigshospitalet Institute of Clinical Medicine Faculty of Medicine University of Copenhagen Copenhagen Denmark

Department of Pediatrics and Pediatric Surgery Hospital de Niños Roberto del Río Facultad de Medicina Universidad de Chile Santiago Chile

Department of Pediatrics and Tettamanti Research Center Fondazione MBBM Ospedale San Gerardo University of Milano Bicocca Monza Italy

Department of Pediatrics Center for Childhood Cancer Research Children's Hospital of Philadelphia Philadelphia PA

Department of Pediatrics Hokkaido University Graduate School of Medicine Sapporo Japan

Department of Pediatrics University Medical Center Schleswig Holstein Kiel Germany

Division of Pediatric Hematology Oncology MacKay Memorial Hospital MacKay Children's Hospital Taipei Taiwan

Great Ormond Street Hospital London United Kingdom; and

Japan Children's Cancer Group Japan Sapporo Japan

Johns Hopkins Kimmel Cancer Center Baltimore MD

Pediatric Hematology and Oncology Department Hospital Sant Joan de Déu de Barcelona Institut de Recerca Sant Joan de Déu Barcelona Spain

Pediatric Hematology Immunology Department University Hospital Robert Debré Assistance Publique Hôpitaux de Paris Université de Paris Paris

Princess Maxima Center for Pediatric Oncology Utrecht The Netherlands

Société Française de Lutte contre les Cancers et Leucémies de l'Enfant et de l'Adolescent Paris France

Translational and Clinical Research Institute Newcastle University Centre for Cancer Newcastle upon Tyne United Kingdom

University Hospital Motol 2nd Faculty of Medicine Charles University Prague Czech Republic

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