Monitoring of minimal residual disease (MRD) by flow cytometry (FCM) is a powerful prognostic tool for predicting outcomes in acute lymphoblastic leukemia (ALL). To apply FCM-MRD in large, collaborative trials, dedicated laboratory staff must be educated to concordantly high levels of expertise and their performance quality should be continuously monitored. We sought to install a unique and comprehensive training and quality control (QC) program involving a large number of reference laboratories within the international Berlin-Frankfurt-Münster (I-BFM) consortium, in order to complement the standardization of the methodology with an educational component and persistent quality control measures. Our QC and quality assurance (QA) program is based on four major cornerstones: (i) a twinning maturation program, (ii) obligatory participation in external QA programs (spiked sample send around, United Kingdom National External Quality Assessment Service (UK NEQAS)), (iii) regular participation in list-mode-data (LMD) file ring trials (FCM data file send arounds), and (iv) surveys of independent data derived from trial results. We demonstrate that the training of laboratories using experienced twinning partners, along with continuous educational feedback significantly improves the performance of laboratories in detecting and quantifying MRD in pediatric ALL patients. Overall, our extensive education and quality control program improved inter-laboratory concordance rates of FCM-MRD assessments and ultimately led to a very high conformity of risk estimates in independent patient cohorts.

1st Department of Pathology and Experimental Cancer Research Semmelweis University 1085 Budapest Hungary

Bioquimica Inmunologia Hospital de Ninos Rocardo Gutierrez Buenos Aires C1425EFD Argentina

Cellular Immunology Laboratory Hospital de Pediatria Dr Juan P Garrahan Buenos Aires C1245 Argentina

Center of Competence PERIMED Department of Pediatrics Department of Microbiology and Clinical Immunology Medical University Plovdiv 4002 Plovdiv Bulgaria

Children's Cancer Research Institute Medical University of Vienna 1090 Vienna Austria

Clinic for Hematology and Tumor Immunology HELIOS Klinikum Berlin Buch 13125 Berlin Germany

Clinica Pediatrica University degli Studi di Milano Biococca Fondazione MBBM 20900 Monza Italy

Clinical Laboratory Diagnostics and Metrology of NCSH OHMATDYT Ministry of Heath of Ukraine 01601 Kiev Ukraine

Department of Clinical Immunology Institute of Pediatrics Jagiellonian University Medical College 31 008 Krakow Poland

Department of Cytopathology Institute of Oncology 1000 Ljubljana Slovenia

Department of Hematology and Oncology Hospital de Pediatria Dr Juan P Garrahan Buenos Aires C1245 Argentina

Department of Hematology University Hospital Schleswig Holstein 24105 Kiel Germany

Department of Immunology and Histocompatibility Agia Sophia Children's Hospital 115 27 Athens Greece

Department of Immunology Aziz Sancar Institute of Experimental Medicine Istanbul University 34452 Istanbul Turkey

Department of Laboratory Medicine University of Debrecen 4032 Debrecen Hungary

Department of Microbiology and Immunology Medical University of Silesia 40 055 Katowice Poland

Department of Oncology and Children's Cancer Research Center University Children's Hospital 8032 Zurich Switzerland

Department of Paediatric Haematology and Oncology University Hospital Motol 150 06 Prague Czech Republic

Department of Pediatric Hematology and Oncology Zabrze Medical University of Silesia 40 055 Katowice Poland

Department of Pediatric Oncology and Hematology Charité Berlin 10117 Berlin Germany

Department of Pediatric Oncology Hippokration General Hospital 546 42 Thessaloniki Greece

Department of Pediatrics University Medical Center SchleswigHolstein Christian Albrechts University of Kiel 24118 Kiel Germany

Division of Laboratory Immunology Department of Laboratory Diagnostics University Hospital Centre Zagreb and School of Medicine 10000 Zagreb Croatia

Division of Pediatric Hematology Oncology Department of Pediatrics Faculty of Medicine University of Debrecen 4032 Debrecen Hungary

Faculty of Medicine University of Ljubljana 1000 Ljubljana Slovenia

Flow Cytometry Laboratory Department of Pathology Clinical Centre University of Pécs 7622 Pécs Hungary

Flow Cytometry Laboratory FUNDALEU Buenos Aires C1114 Argentina

Flow Cytometry Laboratory Provincial Histocompatibility Reference Centre CUCAIBA Buenos Aires C1114 Argentina

Fundación Pérez Scremini Pediatric Hematology Oncology Service Pereira Rossell Hospital Montevideo 11600 Uruguay

Georgios Gennimatas General Hospital of Athens 115 27 Athens Greece

Hematology Lab Sheba Medical Center Ramat Gan 52621 Israel

Hematopathology and Flow Cytometry Division Children's Clinical University Hospital LV 1004 Riga Latvia

Hospital de Clinica Jose de San Martin Buenos Aires C1120 Argentina

Hospital Guillermo Rawson San Juan J5400 Argentina

Hospital Nacional de Clínicas Universidad Nacional de Córdoba Cordoba X5000HUA Argentina

IICT Labs Rosario S2000 Argentina

Laboratorio CEBAC SRL Posadas N3300 Argentina

Laboratory Flow Cytometry Citomlab Buenos Aires C1406AWK Argentina

Laboratory for Flow Cytometry and Immunology Institute for Health and Protection of Mother and Child of Serbia 11070 Belgrade Serbia

Laboratory of Leukemia Immunophenotyping Dmitry Rogachev National Medical Research Center of Pediatric Hematology Oncology and Immunology 117997 Moscow Russia

LEB Laboratorio Servicio de Hematologia Hospital Penna Bahia Blanca B8000 Argentina

M Tettamanti Foundation Research Center Department of Pediatrics University of Milano Bicocca 20900 Monza Italy

National Institute of Children's Diseases 831 01 Bratislava Slovakia

P and A Kyriakou Children's Hospital of Athens 115 27 Athens Greece

PAPSI Laboratorio Mendoza Rosario S2000 Argentina

Pediatric Hematology and Oncology Hospital Sant Joan de Deu 08950 Barcelona Spain

Pediatric Hematology Oncology and Stem Cell Transplant Division Maternal and Child Health Department University of Padova 35122 Padova Italy

PINDA Chilean National Pediatric Oncology Group Hospital Roberto del Rio Universidad de Chile Santiago 8380418 Chile

Servicio de Bioquimica Hospital Posadas Buenos Aires B1684 Argentina

St Anna Children's Hospital Department of Pediatrics Medical University of Vienna 1090 Vienna Austria

The Children's Hospital at Westmead Sydney NSW 2145 Australia

The Rina Zaizov Division of Pediatric Hematology Oncology Schneider's Children's Medical Center Petah Tikva 4920235 Israel

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