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Introduction: Mixed phenotype acute leukemia (MPAL) is a rare subset of acute leukemia where the blasts exhibit lineage specifi c antigens of more than one lineage. Flow cytometric immunophenotyping is essential for the diagnosis of MPAL and the accurate diagnosis highly depends on the panel of markers used. The precise incidence of MPAL is uncertain as various institutions use different combinations of antibodies to assign the blasts to a particular lineage. Aim: The aim was to study the immunoprofi le of acute leukemia including aberrant antigen expressions and to study the incidence, clinical features, laboratory fi ndings, and immunophenotype of MPAL in our institution. Materials and Methods: All cases of acute leukemias in which fl ow cytometric analysis during 1-year period from July 2012 to July 2013 were included in this study. Results: During the study period, fl ow cytometric analysis of 506 cases was performed. B lymphoblastic leukemia was the most common subtype of acute leukemia. CD13 was the most common aberrant antigen expression in acute lymphoblastic leukemia and CD7 was the most common aberrant antigen expression in acute myeloid leukemia. A diagnosis of MPAL was made in 15 cases, which accounted for 2.96% of all leukemias. 9 cases were diagnosed as T/myeloid, 5 cases as B/myeloid and 1 case as B/T. Conclusion: Mixed phenotype acute leukemia is a rare subset of acute leukemia. Flow cytometry is critical in establishing a diagnosis of MPAL. The panel of antibodies used is important in the identifi cation of the “mixed” phenotype. Cytoplasmic markers (cytoplasmic MPO, cytoplasmic 79a, cytoplasmic 22 and cytoplasmic CD3) should be included in the primary flow cytometric panel.
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BACKGROUND: The aberrant, leukemia-associated antigen expression patterns allow us to discriminate leukemic blasts from normal precursor cells. Our major goal was to determine a guideline for the detection of minimal residual disease using CD20+/CD34+ and myeloid Ag+/CD19+ combination in the bone marrow of acute leukemia in complete remission (CR) after chemotherapy. METHODS: Bone marrow samples from 117 patients with acute leukemia in complete remission after chemotherapy and from 22 healthy controls were immunophenotyped by triple staining and measured by flow cytometry. RESULTS: The CD20+/CD34+ cells in the large lymphocyte gate (R1) ranged from 0% to 3.24% (0.8+/-0.82%, P=0.000) in CD20+/CD34+ B-lineage ALL CR (N=31), from 0.03% to 4.2% (0.7+/-0.83%, P=0.000) in CD20-/CD34- B-lineage ALL CR (N=66), from 0.1% to 0.96% (0.45+/-0.32%, P=0.016) in T-ALL CR (N=10), and from 0.02% to 0.48% (0.18+/-0.15%, P=0.776) in AML CR (N=10). The CD13,33+/CD19+ cells in R1 gate ranged from 0% to 2.69% (0.37+/-0.48%, P<0.001) in CD13,33+/CD19+ B-lineage ALL CR (N=31), from 0% to 1.8% (0.31+/-0.28%, P<0.001) in CD13,33-/CD19+B-lineage ALL CR (N=65), from 0.02% to 0.64% (0.29+/-0.22%, P=0.071) in T-ALL CR (N=9), and from 0% to 0.17% (0.07+/-0.09%, P=0.341) in AML CR (N=3). CONCLUSIONS: Using an immunophenotypic method for the detection of early relapse or minimal residual disease of B-lineage ALL bone marrow in CR after chemotherapy, different cutoff values should be applied according to antigen combination and gating. When the proportion of aberrant antigen combination was less than 5% in large lymphocyte gate, the results should be interpreted with caution.