Acute lymphoblastic leukemia with the phenotype of a putative B-cell/T-cell bipotential precursor

Biphenotypic acute leukemias (BALs) are uncommon. Most are of myeloid-B-cell or myeloid-T-cell lineage. We report herein a 70-year-old man with an unusual acute leukemia where the blasts expressed both B- and T-lymphoid markers. He presented to us with an enlarging cutaneous tumor. The presenting peripheral blood and bone marrow aspirate showed 40% and 90% blasts, respectively, which were negative for the usual cytochemical stains. The flow cytometric analysis revealed that the blasts were positive for CD19, CD20, CD22, cytoplasmic (Cyt) CD79a, CD10, Cyt CD3, CD5, CD7, CD4, HLA-DR, TdT, and were negative for myeloid markers. According to the scoring system from the European Group for the Immunological Characterization of Acute Leukaemias (EGIL), this case was an unequivocal B-cell/T-cell BAL. Conventional cytogenetic analysis revealed 46XY [t(4;11)(q31;q13), add(8)(q24), der(9)del(9)(p21)del(9)(q32q34), -13, +mar] in all 25 metaphases analyzed. Fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) for 11q23 rearrangements as well as t(9;22) were negative. PCR for both TCR-gamma and IgH gene analyses revealed polyclonal rearrangements. We postulate that this case of BAL might have arisen from the putative common lymphoid progenitor cell.