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

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 specialised working groups including the European Hematology Association (EHA) Diagnosis in Hematological Diseases Specialised Working Group and the European LeukemiaNet (ELN) produced consensus guidance for harmonised blast assessment to define response categories in acute leukemic patients. These address 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.