1. ICCS Case of the Quarter
65 year old male with soft tissue mass in the thigh
No significant past medical history
Blood pressure medication only
A biopsy of the soft tissue mass was performed, with subsequent bone marrow evaluation.
CBC
WBC 4.8
Hct 52.4
Plt 189

2. Bone marrow: flow cytometry

3. Antibodies and Fluorochromes
PB*
BV421#
FITC PE
PE-TR*
PE -CF594#
PE Cy5*
PE Cy55#
PE Cy7
A594
APC
APC-A700
APC-H7
HLA-DR*
CD15
CD33
CD19#
CD117*
CD13
CD38
CD34
CD71
CD45
CD64
CD123
CD4*
CD14#
CD16
Kappa
Lambda
CD5#
CD19
CD10
CD8#
CD2
CD5
CD34#
CD56*
CD3
CD4
CD7
CD30
cMPO
cCD79a
cCD3*
Tubes M1 M2 B T
Cytoplasmic

4. Starting Point 2. 1. 3.
We start by obtaining single cell data on all events, avoiding cell clumps, by gating on “singlets” based on forward scatter height (FSC-H) versus area characteristics (FSC-A).
Next we focus on the “singlet gate,” and gate based on FSC-A and side scatter height(SSC-H) characteristics in order to obtain viable events, and also exclude nucleated red cells.
Now we have white cell data, and we gate on the viable cellular components based on CD45 versus SSC-H characteristics to divide into cell types.
Blue arrow is the lymphocyte gate
Green arrow is the myeloid and monocytic gate
Red arrow is the blast or immature gate.

5. Next: Focus on the dim CD45 / blast gate (RED events)1. 2.
CD45 vs SCC defined
Blast gate
The events in the dim CD45 vs SCC defined blast region are highlighted in red, and negative for CD34 and CD19,
Looking at all WBCs for expression of CD117, the RED, dim CD45 population is essentially negative for CD117

6. Myeloid tubes, M1 and M2
In the the myeloid tubes the dim CD45, Red population is:
Positive for low CD4, CD33, CD38, subset low CD71, bright CD123, and HLA-DR
Negative or essentially negative for CD15, CD16, CD19, CD34 and CD64. CD13, CD14 and CD117 may show small subset expression, but are overall negative

7. B and T cells tubes
The B and T cell tubes show the dim CD45, Red population is positive for CD56 (intermediate to bright) with low CD4, low to intermediate CD7 and negative for CD2, CD3, CD5, CD8, CD10 and CD20

8. Cytoplasmic tube Phenotype by flow cytometry
The cytoplasmic tube shows that the dim CD45, Red population is negative for cCD3, cCD79a and cMPO.
There is spill over of maturing myeloid cells from the myeloid gate (blue arrow) into the dim CD45 gate, which is colored aqua in the dim CD45 gated dot plots.
Phenotype by flow cytometry
Positive: CD4 (low), CD7 (low to intermediate), CD13 (subset low), CD33, CD38, CD45 (dim), CD56 (intermediate to bright), CD71 (subset low), CD123 (bright) and HLA-DR
Negative (or essentially negative): CD2, CD3 (surface and cytoplasmic), CD5, CD8, CD10, CD13, CD14, CD15, CD16, CD19, CD20, CD34, CD64, cCD79a, CD117, cMPO

9. Soft tissue mass (thigh): morphology

10. Soft tissue touch prep, Wright-Geimsa, 40x
Numerous, monotonous large mononuclear cells
-Moderate amount of cytoplasm, some with vacuoles, no granules
-Nuclei round/oval to folded with smooth/delicate chromatin, some with nucleoli

11. Soft tissue touch prep, Wright Geimsa, 100x

12. H&E, 40x
Diffuse sheets of intermediate to large mononuclear cells
-Scant to moderate amount of cytoplasm
-Nuclei round/oval to folded, some elongate, with smooth chromatin
-Some with nucleoli
Blue arrow points to reactive lymphocytes for comparison

13. H&E, 63x

14. Immunohistochemistry
TCL-1 positive, 10x
TDT positive, 10x

15. Diagnosis: Blastic plasmacytoid dendritic cell neoplasm (BPDCN)
Involving the skin and marrow
Flow cytometry: positive CD4 (low), CD7 (low to intermediate), CD33, CD38, CD45 (dim), CD56 (intermediate to bright), CD71 (subset low), CD123 (bright) and HLA-DR
Immunohistochemistry: positive for TCL-1 and TDT

16. Blastic plasmacytoid dendritic cell neoplasm (BPDCN)
Although lineage had previously been under debate, it is now classified with acute myeloid leukemia in the 2008 WHO classification.
Synonyms / historical designations: Agranular CD4/CD56 positive hematodermic neoplasm, Blastic NK cell leukemia/lymphoma

17. BPDCN cell of origin
Plasmacytoid dendritic cell (PDC) / plasmacytoid monocyte
Small numbers are normally present in peripheral blood/marrow and lymphoid tissues (primary and secondary) with proliferations occurring in various disease states
Such as Toxoplasmosis, Castleman’s and various hematopoietic and non-hematopoietic neoplasms
Normal PDCs express CD123 and lack CD56
Although a minor population of normal CD56 positive PDC-like cells have been noted in the peripheral blood and marrow
0.03% of peripheral blood mononuclear cells

18. BPCDN Clinical Presentation
Usually occurs in the the 6th decade (although can occur at any age, including pediatric cases).
Typically presents with cutaneous lesions, which often include marrow involvement
Fewer cases will lack dermal involvement, presenting with a leukemic picture
Some cases will involve marrow and skin without blood involvement
Cutaneous lesions may vary from small plaques and nodules to large plaques/tumors with variable pigmentation (tan/brown – red – blue/purple)
May have a bruise-like appearance
May be single or multiple

19. BPDCN morphology Blast or blast-like morphology
Intermediate to large mononuclear cells with round/oval nuclei, may have nuclear irregularity or folding
Scant to moderate amount of agranular cytoplasm, may have vacuoles (typically localize along cell membrane)
Smooth/delicate/fine chromatin, often with nucleoli
“Leukemic” type of infiltration in skin and lymph nodes
Dermal infiltrate, perivascular and periadnexal which does not involve the epidermis. Progresses to diffuse sheets in the dermis / subcutaneous tissues.
Early lymph node involvement of medullary and sinus regions progressing to infiltration of the cortical/paracortical regions. Diffuse sheets with progression.

20. BPDCN Immunophenotype
Typical phenotype:
expression of CD4, CD38, CD43, CD56, CD123 (typically brighter than monocytes), TCL1, CD303 (BDCA-2), CD2AP and HLA-DR
CD7, CD33, CD68, TdT and S100 expression can be seen.
lack of surface and cytoplasmic CD3, CD5, CD13, CD14, CD15, CD16, CD19, CD20, CD34, CD64, CD117, EBER, Lysozyme, MPO, NSE, TIA-1

21. BPDCN Immunophenotype
The five most characteristic markers are CD4, CD56, CD123, CD303 and TCL1
Non typical phenotypic findings
Although typically negative, low CD2 or CD13 may be seen
Weak expression of CD4 or CD56 (and extremely rare lack of CD56 and/or CD4) has been reported
If lacking CD56, exclusion of proliferating mature plasmacytoid dendritic cells must be excluded

22. BPDCN cytogenetics/molecular
No specific cytogenetic or molecular alterations
Often has a complex karyotype
Frequent deletions of TP53, CDKN2A, CDKN1B, RB1, TET2, PTEN (tumor suppressor genes)

23. BPDCN Clinical Course Extremely poor prognosis in adults
Usually responds to therapy, but quickly relapses
Average overall survival months
Variable chemotherapeutic regimens have been used, including CHOP*, ALL type induction and AML type induction regimens
Although most patients will respond initially to chemotherapy, many will relapse
Best treatment protocol is not known; however, long term survival in adults appears best achieved with stem cell transplant in first remission.
BPDCN is clinically less aggressive in children
Typically treated with a high-risk ALL type regimen
Stem cell transplant may be reserved for those who relapse in second remission
*CHOP – cyclophosphamide, doxorubicin, vincristine, prednisone

24. Differential diagnosis
NK cell neoplasm
Acute Monocytic/Myeloid leukemia (AMoL/AML)
Similar to BPDCN, NK cell neoplasms will express CD43 and CD56
Unlike BPDCN, NK cell neoplasms will lack CD4, CD123, TCL1, TdT
Although CD7 can be expressed in both NK cell neoplasms and BPDCN, CD7 is typically brighter and more uniform in NK cell neoplasms
NK cell neoplasms will express EBER and BPDCN will be negative
Similar to BPDCN, AMoL will often express CD4, CD33 and HLA-DR, may express CD56 and typically lack CD14.
Unlike BPDCN, AMoL lacks TCL1, CD303 (BDCA-2) and express bright CD64 and lysozyme.
Although CD123 is expressed in both AMoL and BPDCN, CD123 is typically brighter in BPDCN.
AML will often express CD34 and/or CD117, where BPDCN will be negative

25. References
Swerdlow SH, et al. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues, IARC, Lyon, p145-47, 2008.
Cherian S, Wood B. Flow Cytometry in evaluation of hematopoietic neoplasms: A case-based approach, CAP press, IL, p152-55, 2012.
Laribi K, et al. “Blastic Plasmacytoid Dendritic Cell Neoplasm: From Origin of the cell to Targeted therapy; Biol Blood Marrow Transplant, 1-11, 2016.
Yang S, Wang E. Blastic Plasmacytoid Dendritic Cell Neoplasm: A clinicopathologic review, Arch Pathol Lab Med; 138, 564-9, 2014.
Julia F, et al. Blastic Plasmacytoid Dendritic Cell Neoplasms: Clinico-immunohistochemical Correlations in a Series of 91 Patients, Am J Surg Pathol; 38(5)673-80:2014.
Riaz W et al. Blastic Plasmacytoid Dendritic Cell Neoplasm: Update on Molecular Biology, Diagnosis and Therapy, Cancer Control; 21(4)279-89:2014.
Jegallan A, et al. Blastic plasmacytoid dendritic cell neoplasm in children: diagnostic features and clinical implications, haematologica, 95(11)1873-9: 2010.
Osaki Y et al. Characterization of CD56+ dendritic-like cells: a normal counterpart of blastic plasmacytoid dendritic cells neoplasm?, PLoS One, 8(11)e8172:2013