Definitive Criteria for Ambiguous Lineage Leukemias

Abstract

Biphenotypic leukemias are acute leukemias of ambiguous lineage in which there is proliferation of more than one distinct cell type. In this case, both myeloid and lymphoid phenotypes are present in the blast population. As opposed to leukemias in which one specific myeloid or lymphoid population is found, these biphenotypic leukemias present a unique diagnostic challenge in these patients. Treatment is determined by identification of the predominant lineage. This study explores the successful use of the European international scoring system to define biphenotypic acute leukemias. Of nine cases of leukemias of mixed phenotype, determined by flow cytometric analysis, three were scored as biphenotypic by traditional 2001 WHO standards, whereas six were of ambiguous lineage but did not meet the scoring criteria for mixed phenotype. However, on re‐evaluation using the 2008 WHO guidelines, three of these cases were reclassified as biphenotypic based on the increased significance of myeloperoxidase (MPO) and combined CD14/CD64 positivity for myeloid lineage. Considering the worse prognosis of biphenotypic leukemia than AML or ALL, early identification of mixed lineage is critical for appropriate treatment.