Mixed acute leukemia with genotypic lineage switch: A case report

Morphologically well classifiable leukemias can reveal a mixed phenotype. A case of acute myeloid leukemia (CD13, CD33, CD14, CD11b) which at presentation showed a co-expression of B-lymphoid markers (CD19, CD10, CD20), at the time of the first relapse revealed a morphologic, phenotypic and genotypic switch of the blasts to a purely lymphoid form. Analysis of the immunoglobulin (Ig) H chain locus and of the T-cell receptor (TCR) genes showed at diagnosis a germline configuration of the IgH, TCRβ and γ genes, and a deletion of the TCR δ gene at the second chromosome. At relapse, monoclonal rearrangements of the IgH, TCR γ, and TCR δ were detected. At a subsequent relapse, the blasts re-expressed myeloid morphologic features and myeloid-associated antigens, while they retained the same rearranged configuration of the IgH and TCRβ and δ genes. The TCR δ gene configuration, which links each phase of the disease, may represent an early pathogenetic event and makes the emergence of a second malignancy unlikely. Each phenotypic change occurred after anti-myeloid and anti-lymphoid oriented chemotherapy. The close correlation between the progressive acquisition of different phenotypes and the switch at the genomic level represent the peculiar features of this unusual case.