OBJECTIVES: Risk-based stratification approaches using measurable residual disease (MRD) successfully help to identify T-acute lymphoblastic leukemia (T-ALL) patients at risk of relapse, whose treatment outcomes are very poor. Because of T-ALL heterogeneity and rarity, a reliable and standardized approach for flow cytometry (FC)-based MRD measurement and analysis is often missing. METHODS: Within the international AIEOP-BFM-ALL-FLOW study group we made a consensus on markers and a standard operating procedure for common 8- and 12-color T-ALL MRD panels. Custom manufactured tubes with dried backbone antibodies were tested in parallel to local FC standards. RESULTS: Altogether, 66 diagnostic and 67 day 15 samples were analyzed. We designed two guided MRD gating strategies to identify blast cells in parallel to expert-based evaluation. We proved that the optimized tubes allowed the correct identification of blast cells in all diagnostic samples. Both, expert and guided analysis of day 15 samples correlated to local standard (Spearman R=0.98 and R=0.94, respectively). Only in 2 (3 %) and 4 (6 %) patients expert gating and guided analysis results were substantially discordant from local standard, respectively. The cases that require an individualized approach may be partially identified at diagnosis through a rare immunophenotype or mixed phenotype acute leukemia status. CONCLUSIONS: Our work shows that standardized operating procedures together with guided analysis are applicable in a great majority of T-ALL cases. Further improvement of MRD detection is needed, as in some cases an individualized analytical approach is still required due to the challenging nature of the T-ALL phenotype.

CLIP Prague Czech Republic

Department of Hematology University of Schleswig Holstein Kiel Germany

Department of Laboratory Medicine National Institute of Children's Diseases Bratislava Slovakia

Department of Molecular Medicine University of Padua Padua Italy

Department of Paediatric Haematology and Oncology 2nd Faculty of Medicine Charles University Prague Czech Republic

Department of Pediatric Hematology and Oncology National Institute of Children's Diseases Bratislava Slovakia

Department of Pediatrics and Adolescent Medicine St Anna Children's Hospital Medical University of Vienna Vienna Austria

Labdia Labordiagnostik Vienna Austria

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

Pediatric Onco Hematology Stem Cell Transplant and Gene Therapy Laboratory Istituto di Ricerca Pediatrica Città della Speranza Padua Italy

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

Sheba Medical Center Hematology Lab Tel Hashomer Israel

St Anna Children's Cancer Research Institute Vienna Austria

Tettamanti Center Fondazione IRCCS San Gerardo dei Tintori Monza Italy

University Hospital Motol Prague Czech Republic

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