Reporting blast percentage for response assessment in acute leukemias: recommendations from an EHA/ELN expert panel

Sep 29, 2026

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Evaluation of bone marrow blast percentage is critical for response criteria in acute leukemias. The article addresses inconsistencies in laboratory methodologies and provides international consensus guidance from EHA and ELN expert working groups to harmonize blast assessment. It covers sampling best practices, accurate blast enumeration, and limitations across ALL, AML, and acute leukemia of ambiguous lineage. Integrated reporting schemes use morphological cross-check alongside measurable residual disease assays to support uniform standards in trials and routine care.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

Abstract

Introduction

Sampling

GUIDELINE ARTICLE Reporting blast percentage for response assessment in acute leukemias: recommendations from an EHA/ELN expert panel Sa A. Wang,1 Leonor Arenillas,2 Francesco Buccisano,3 Monika Bruggemann,4 Wolfgang Kern,5 Manuel Menes,6 Adriana Plesa,7 Louisa Stone,8 Dominique Wellnitz,4 David A. Westerman,9 Brent L. Wood10 and Sylvie D. Freeman11 1 Department of Hematopathology, MD Anderson Cancer Center, Houston, TX, USA; 2 Department of Pathology, Hospital del Mar, Barcelona, Spain; 3 Department of Biomedicine and Prevention, University Tor Vergata, Rome, Italy; 4 Medical Department II, Hematology and Oncology, University Hospital Schleswig-Holstein, Kiel, Germany; 5 MLL Munich Leukemia Laboratory, Munich, Germany; 6 Department of Pathology, Baptist Health South Florida, Miami, FL, USA; 7 Department of Hematology Laboratory and Flow Cytometry, Lyon University Hospital, CHU-HCL, Lyon Sud, Pierre Benite, France; 8Auckland City Hospital, Auckland, New Zealand; 9 Department of Pathology, Peter MacCallum Cancer Centre, Melbourne, Australia; 10 Department of Pathology and Laboratory Medicine, Children’s Hospital of Los Angeles, Los Angeles, CA, USA and 11School of Infection, Inflammation and Immunology, University of Birmingham, Birmingham, UK Abstract Correspondence: S. D. Freeman [s.freeman@bham.ac.uk](s.freeman@bham.ac.uk) Received: May 15, 2025. Accepted: August 8, 2025. Early view: September 4, 2025. [https://doi.org/10.3324/haematol.2025.288228](https://doi.org/10.3324/haematol.2025.288228) ©2026 Ferrata Storti Foundation Published under a CC BY-NC license Evaluation of bone marrow blast percentage is paramount to response criteria in acute leukemias. There is an identified need within the framework of updated laboratory practices to reduce inconsistencies in methodologies used by clinical laboratories to report blast values and clarify aspects of reporting. Representatives from international specialized working groups including the European Hematology Association (EHA) Diagnosis in Hematological Diseases Specialized Working Group and the European LeukemiaNet (ELN) produced consensus guidance for harmonized blast assessment to define response categories in patients with acute leukemia. This guidance addresses sampling best practice, key considerations for generating the most accurate blast enumeration and the limitations across the methodologies in acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML) and acute leukemia of ambiguous lineage. An integrated reporting scheme for deriving blast percentage is provided for ALL and AML. This incorporates results from appropriate measurable residual disease assays with morphological crosscheck. The practical guide and approach presented herein should facilitate uniform reporting standards both within clinical trials and in broader clinical practice. Introduction Evaluation of therapeutic response in acute leukemia requires a documented bone marrow (BM) blast percentage. According to the International Working Group (IWG 2003) criteria,1 this percentage is determined based on a morphological blast count. Although this method has been widely used in clinical practice over the years, it is recognized as imperfect because of its subjective nature, limited ability to distinguish non-neoplastic from leukemic blasts, and significant interoperator variation, even among experts. Over the past two decades, clinical laboratory practices have evolved with advancements in integrated reporting, clinical flow cytometry and access to measurable residual disease (MRD) assays. Strong evidence supports MRD assays in measuring treatment response in acute leukemias.2-10 Such assays are intended to directly identify residual leukemia for which morphological blasts are a surrogate. There does, however, remain uncertainty in defining blasts for response categories with concerns in the community regarding a certain lack of standardization in how blast percen

FAQs

Why is bone marrow blast percentage evaluation important in acute leukemias?

It is essential for applying response criteria and for ensuring reliable response assessment. The article emphasizes that inconsistencies in how blast values are reported can affect clinical decisions and trial outcomes.

What are the main problems with morphological blast counting alone?

Morphological assessment is described as imperfect due to its subjective nature, limited ability to distinguish non-neoplastic from leukemic blasts, and significant inter-operator variation.

How does the guidance improve blast percentage reporting across laboratories?

It provides harmonized recommendations on sampling and blast enumeration, and proposes integrated reporting for ALL and AML that incorporates measurable residual disease assays with morphological cross-check to improve accuracy and comparability.

Sep 29, 2026

Upload by Riley