Case 7: Acute myeloid leukemia
Clinical Vignette
72-year-old woman with newly developed anemia and unclassified cells on peripheral blood smear. A bone marrow sample is submitted for flow cytometric immunophenotyping using ClearLLab 10C Panels.
Flow Cytometric Immunophenotyping
M1 Cell Tube
Figure M1-04. This CD45 vs Side Scatter dot plot shows events in the Cells gate. This plot is intended to highlight various subsets of white blood cells, which are gated as CD45 positive. The CD45 negative population (Gray colored events) usually includes red blood cells, platelet aggregates, tissue debris or nonhematopoietic cells.
Figure M1-05. This CD45 vs Side Scatter dot plot shows events in the CD45+ gate. This dot plot permits distinction of several white blood cell populations typically found in peripheral blood, bone marrow, and lymph node samples, including lymphocytes (Gate Ly, red), monocytes (Gate Mo, green), and granulocytes (Gate Gr, blue). The CD45dim gate (purple) covers the area typically occupied by early progenitors (e.g., myeloblasts and immature B cells). Basophils, plasmacytoid dendritic cells, plasma cells and NK cells may also appear in this area. By applying different colors to the events comprised by each gate, the various populations may be identified throughout the analysis. Of note, cells in the CD45dim and monocyte gates are expanded.
Figure M1-11. This CD34 vs Side Scatter dot plot shows all viable cells. CD34 is a marker of early hematopoietic progenitors. It is expressed on hematopoietic stem cells, early myeloid progenitors (myeloblasts), and immature B and T cells (lymphoblasts). CD34 positive progenitors typically have low to intermediate side scatter in the CD45 dim gate (purple) with immature B cell progenitors having lower side scatter than immature myeloid progenitors.
Figure M1-16. This CD16 vs CD13 dot plot shows all viable cells. CD13 is expressed on maturing granulocytes (blue), monocytes (green), basophils, and CD34+ progenitors (purple). CD16 is expressed on maturing granulocytes (blue) and a subset of NK cells (red). During granulocytic maturation, CD13 is expressed variably by promyelocytes without CD16 (blue left) and lose CD13 as they mature to myelocytes (blue bottom left). Myelocytes then simultaneously acquire CD13 and CD16 as they mature from metamyelocytes having low CD16 to mature granulocytes having high expression of both CD13 and CD16 (blue top right).
Figure M1-17. This CD13 vs CD34 dot plot shows all viable cells. CD13 is expressed on maturing granulocytes (blue), monocytes (green), basophils, and CD34 positive progenitors (purple). CD34 is expressed on early hematopoietic progenitors. CD13 is not well expressed on CD34 positive B cell progenitors (purple) or mature lymphoid cells (red). Of note, the CD34 positive blasts are partially positive for CD13.
M2 Cell Tube
Figure M2-08. This CD117 vs Side Scatter dot plot shows all viable cells. CD117 is expressed variably on CD34+ myeloid progenitors, early promyelocytes, and early erythroid precursors, and at a high level on mast cells (blue right). CD117 is also expressed on subsets of reactive NK cells and neoplastic plasma cells. Note most of the blasts (in purple) are CD117 positive.
Figure M2-10. This CD33 vs Side Scatter dot plot shows all viable cells. CD33 is expressed at its high level on immature and mature monocytes (green), at a slightly lower level on immature granulocytes (blue), and at the lowest level on mature granulocytes (blue). CD33 is also expressed on basophils, a subset of NK cells (red), and a subset of CD34+ myeloid progenitors (purple). Note the blasts (purple) are CD33 positive.
Figure M2-13. This HLA-DR vs Side Scatter dot plot shows all viable cells. HLA-DR is expressed on antigen presenting cells including monocytes (green) and plasmacytoid dendritic cells. It is also expressed on CD34 positive progenitors (purple), mature (red) and immature (purple) B cells, and activated T cells (red).
Flow Cytometry Result Interpretation
The flow cytometry study detected expanded myeloid blasts and monocytes. The blasts are in the CD45dim gate and express CD33, CD34, CD117 and HLA-DR. The blasts also abnormally express CD10 and CD56 (in a subset), while negative for CD19. The expanded monocytes are positive for CD13, CD14 and CD64 with increased CD56 in a subset. Together, the flow cytometry results support acute myelomonocytic leukemia.