PMC6330528_01
The figure shows ulcerated skin nodule on the chest wall of case 1. The other two patients also had similar skin lesions.
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No lymphadenopathy was detected (figures 1 and 2). 
Multiple blasts (arrows) admixed with erythroid precursor cells (arrow heads) (bone marrow imprint, Wright-Giemsa stain, x1000). Insert shows a blast in the concurrent peripheral blood (Wright-Giemsa stain, original magnification: x1000). The blasts are medium-sized cells with irregular nuclei and scant cytoplasms which cannot be morphologically recognized as neoplastic dendritic cells. These images are related to case 1.
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No lymphadenopathy was detected (figures 1 and 2).  Bone marrow aspiration and biopsy were consistent with peripheral blood and demonstrated hypercellularity with about 41% blast cells (figure 2).
PMC6330528_02
Blast cells are separated from the epidermis by a well-defined Grenz zone (double-arrow) (upper left, H&E, x200)(A); Monomorphic medium-sized blast cells with irregular nuclei (upper right, H&E, x400)(B); Positive membranous CD56 immunostaining (lower left, x200)(C); Positive cytoplasmic CD123 immunostaining (lower right, x200)(D). Since CD123 is a specific marker for plasmacytoid dendritic cells, this positive result is a key finding without which an accurate diagnosis cannot be made. These images are related to case 2.
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In addition, the Ki-67 proliferation index was 40% (Figure 3c and 3d). 
Flow cytometry characteristics of BPDCN in a patient with about 90% blasts in bone marrow. The blasts are positive for CD45, CD4, CD56, HLA-DR, and negative for CD3, B-markers (CD19 and CD10), CD13, and CD14. Selecting a pertinent panel needs high suspicion for this neoplasm. These images are related to case 2.
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Figure 4 illustrates the key flow cytometry findings. 
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