Michael Cubbage

Detection of Lymphoid and Myeloid Lineages in Infantile B-Cell Acute Lymphoblastic Leukemia With Mixed-Lineage Leukemia Rearrangement by Use of Flow Cytometry and Cytogenetic Analysis

Switch between lymphoid and myeloid cell lineage by a leukemic clone is an event with particularly poor prognostic significance. Lineage switch is not common and has previously been described by isolated case reports. Recently, a large, single-institution series drew attention to the association of this phenomenon with MLL (myeloid/lymphoid or mixed-lineage leukemia) abnormalities and highlighted the importance of differentiating between progression of original disease and evolution of treatment-associated malignancy. In this series, all patients who exhibited lineage switch died of disease, underlining the critical need for early recognition and stratification when making treatment decisions among this group. Flow cytometric monitoring has proven to be more sensitive and accurate than routine morphologic screening in evaluation for minimal residual disease and in tracking progression of leukemic clones. The present case illustrates how this methodology can augment detection and monitoring of leukemia that converts in lineage. This report emphasizes the importance of early recognition of the entity.