Examples of immunophenotypic analysis of myeloid blasts in low- and intermediate-I–risk MDS. (A) Forward light scatter (FSC) and sideward light scatter (SSC) properties of a bone marrow sample of a myelodysplastic syndrome (MDS) patient are depicted (unique patient numbers are depicted in lower left corners). FSC (x-axis) and SSC (y-axis) reflect size and granularity, respectively. (B) CD45 staining (x-axis) versus SSC (y-axis) in this patient; CD45 is expressed on all white blood cells (highlighted in dark gray and black). CD34⁺ myeloid blasts, characterized by their diminished level of CD45 and low-to-intermediate SSC, are highlighted in black in all panels. (C-I) CD34 is depicted on the y-axes and lymphoid markers on the x-axes. Fluorescence 1 (FL1), FL2, FL3, and FL4 indicate fluorescein isothiocyanate–, phycoerythrin-, peridinin-chlorophyll protein–, and APC-conjugated antibodies, respectively. Solid gray lines indicate expression levels of lymphoid markers CD5, CD7, and CD56 in the reference lymphocyte population (x-axes in panels C-I). (D) The natural killer cell population was too small to generate a contour line; therefore, the reference population is depicted as gray dots. Marker expression was compared with unstained cells or appropriate isotype controls. Dashed black lines are depicted in case more than 20% of myeloid blasts expressed a lymphoid marker (aberrant flow cytometry); percentages of aberrant blasts are indicated as percentage of CD34⁺ cells. R indicates Epo responder; and NR, nonresponder. Graphs were generated with the use of Infinicyt software (Cytognos).