Mixed phenotype acute leukemia (MPAL) encompasses a heterogeneous group of rare leukemias in which assigning a single lineage of origin is not possible. A variety of different terms and classification systems have been used historically to describe this entity. MPAL is currently defined by a limited set of lineage-specific markers proposed in the 2008 WHO monograph on classification of tumors of hematopoietic and lymphoid tissues. In adult patients MPAL is characterized by relative therapeutic resistance that may be attributed in part to the high proportion of patients with adverse cytogenetic abnormalities. No prospective, controlled trials exist to guide therapy. The limited available data suggests that an 'acute lymphoblastic leukemia-like' regimen followed by allogeneic stem cell transplant may be advisable; addition of a tyrosine kinase inhibitor in patients with t(9;22) translocation is recommended. The role of immunophenotypic and genetic markers in guiding chemotherapy choice and post remission strategy as well as the utility of targeted therapies in non-Ph positive MPALs are unknown.
Ofir Wolach and Richard M. Stone,