Defining Mixed Phenotypic Leukemias

The majority of acute leukemias can be classified by the lineage of origin of blast cells as either myeloid, B Lymphoblastic (B-ALL) or T lymphoblastic. Acute leukemias are categorized by flow cytometry and now, increasingly, molecular results which help to determine whether the leukemia arises from the myeloid or lymphoid series. There does exist, however, an undefined or ambiguous group of leukemias in need of further characterization. Previous World Health Organization (WHO) criteria had defined a population of leukemic cells with no clear lineage restricting markers as Acute Undifferentiated Leukemias (AUL). Mixed Phenotypic Acute Leukemias (MPAL) represent a relatively new diagnostic designation, only being formally recognized and defined by the World Health Organization in 2008 [1]. Given the short time that these formal criteria have been established and the rarity of MPAL, there is a paucity of data regarding the precise biologic characterization of the disease as well as established guidelines on the management and prognosis of these patients. Herein, we review the defining characteristics, cytogenetic and clinical features and potential treatment options available for these patients.