Acute Leukemias of Ambiguous Lineage

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Acute leukemias of ambiguous lineage (also known as acute leukemias of undetermined lineage, mixed phenotype acute leukemias, mixed lineage acute leukemias, and hybrid acute leukemias) are types of acute leukemia in which the morphologic, cytochemical, and immunophenotypic features of the blast population do not allow classification in myeloid or lymphoid categories; or the types have morphologic and/or immunophenotypic features of both myeloid and lymphoid cells or both B and T lineages (i.e., acute bilineal leukemia and acute biphenotypic leukemia).


These rare leukemias account for less than 4% of all cases of acute leukemia and occur in all age groups but are more frequent in adults.  Clinical features include symptoms and complications caused by cytopenias, i.e., fatigue, infections, and bleeding disorders.

Possible causes

Similar to other acute leukemias the aetiology is unknown. Environmental toxins and radiation exposure are possible causes.


Acute biphenotypic and acute bilineal leukemia may present either as one of the subtypes of AML or with features of acute lymphoblastic leukemia. in some cases the blasts are morphologically undifferentiated.