Case 2: Chronic lymphocytic leukemia/small lymphocytic lymphoma
Clinical Vignette
This 68-year-old male presents with anemia and lymphocytosis. A peripheral blood sample is submitted for flow cytometric immunophenotyping using ClearLLab 10C Panels.
Flow Cytometric Immunophenotyping
B Cell Tube
Figure B03. This Side Scatter vs Forward Scatter dot plot shows events in the Singlets gate. This plot is intended to exclude cell debris, which usually has decreased forward scatter with increased side scatter. Early apoptotic cells also have mildly increased side scatter while late apoptotic and necrotic cells have variably decreased side scatter. Viable cells are included in the Cells gate.
Figure B04. 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 non-hematopoietic cells.
Figure B05. 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/orange), 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 followed throughout the analysis.
Figure B06. This CD19 vs Side Scatter dot plot shows events in the Cells gate. The CD19+ gate identifies CD19 positive cells (orange). CD19 is expressed on mature and immature B cells, as well as most plasma cells. These cells typically have low to moderate side scatter. Note the relatively increased number of CD19 positive B cells in this sample.
Figure B15. This Lambda vs Kappa dot plot shows all CD19+ cells. The mature B cells are polyclonal, expressing either kappa or lambda light chain. The normal kappa to lambda ratio is ~1.4 with a range between 1 to 2. The CD19 positive cells (orange) predominantly have surface lambda light chain expression at a decreased level compared with normal mature B cells, indicating a clonal B cell population. A small population of polyclonal B cells (also in orange) with normal levels of kappa and lambda light chain expression is present.
Figure B16. This CD19 vs. CD20 dot plot shows all cells in the lymphocyte gate (Ly). Mature B cells express both CD19 and CD20. Some neoplastic B cells may show decreased CD19 or CD20 expression. The clonal B cells (orange) display decreased CD19 and CD20 expression compared with the higher level seen on normal mature B cells (orange, upper middle).
Figure B20. This CD19 vs CD5 dot plot shows all cells in the lymphocyte gate (Ly). CD5 is expressed on T cells (red), variably expressed at a low level on a subset of normal mature B cells, and expressed on some subtypes of neoplastic B cells. The clonal B cell population (orange) expresses CD5 and CD19. The small population with normal CD19 and low to absent CD5 expression (also in orange, lower middle) represents normal B cells.
Figure B21. This CD20 vs CD200 dot plot shows all cells in the lymphocyte gate (Ly). Most mature B cells (orange) express CD200 at a low to moderate level. The clonal B cell population (orange) expresses CD200 and variably decreased CD20. The small population with normal CD20 and CD200 expression (also in orange, right) represents normal B cells.
Flow Cytometry Result Interpretation
Flow cytometric immunophenotyping identifies a phenotypically distinct population of cells with expression of intermediate to bright CD5, intermediate CD19, low to intermediate CD20, low to absent CD38, bright CD45, intermediate CD200, and dim surface lambda light chain expression without CD10, or other T cell or myeloid antigens. Compared with normal B cells, the expression of CD5, decreased CD20, and lambda light chain restriction of low intensity are aberrant.
Taken together, the immunophenotype of the aberrant population is most consistent with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). However, a definitive diagnosis of CLL/SLL using current WHO criteria requires the demonstration of disease-related clinical and/or laboratory findings and/or the presence of greater than 5,000 neoplastic cells per microliter in the peripheral blood. Therefore, correlation with clinical and laboratory data is recommended, and that additional immunophenotyping may be warranted.