CD56(+) TdT(+) blastic natural killer cell tumor of the skin: a primitive systemic malignancy related to myelomonocytic leukemia

Tagraxofusp, a first-in-class CD123-targeted agent: Five-year postapproval comprehensive review of the literature

Tagraxofusp is a first-in-class CD123-directed conjugate of an amended diphtheria toxin platform and recombinant interleukin 3. Binding and subsequent internalization of the drug result in cell death via disruption of intracellular protein synthesis. CD123 is a surface marker that is expressed in several hematological malignancies, especially blastic plasmacytoid dendritic cell neoplasm (BPDCN), where its expression is ubiquitous. A pivotal study of tagraxofusp in BPDCN resulted in its approval for the treatment of BPDCN, the first treatment approved for this indication. Since the introduction of tagraxofusp, research has focused on the management of adverse effects, combination therapy to improve outcomes in fit patients, and dosing and combination strategies to mitigate toxicities while preserving efficacy, especially among older patients. The successful targeting of CD123 in BPDCN has also encouraged research into a variety of other CD123-positive hematological neoplasms, including acute myeloid leukemia (AML), and informed the development of other novel agents targeting CD123. This review examines the clinical data leading to the development and approval of tagraxofusp in BPDCN, how it is being used in combination to improve outcomes in BPDCN and AML, and its developing role in other hematological malignancies.

Cutaneous Manifestations of Myeloid Neoplasms Exhibit Broad and Divergent Morphologic and Immunophenotypic Features but Share Ancestral Clonal Mutations With Bone Marrow

In this study, we performed a comprehensive molecular analysis of paired skin and peripheral blood/bone marrow (BM) samples from 17 patients with cutaneous myeloid or cutaneous histiocytic-dendritic neoplasms. The cutaneous manifestations included 10 patients with cutaneous acute myeloid leukemia (c-AML), 2 patients with full or partial Langerhans cell differentiation, 2 patients with blastic plasmacytoid dendritic cell neoplasms (BPDCN), 1 patient with both Langerhans cell differentiation and BPDCN, and 2 patients with full or partial indeterminate dendritic cell differentiation. Seven of the 10 c-AML patients (70%) exhibited concurrent or subsequent marrow involvement by acute myeloid leukemia, with all 7 cases (100%) demonstrating shared clonal mutations in both the skin and BM. However, clonal relatedness was documented in one additional case that never had any BM involvement. Nevertheless, NPM1 mutations were identified in 7 of the 10 (70%) of these c-AML cases while one had KMT2A rearrangement and one showed inv(16). All 3 patients (100%) with Langerhans cell neoplasms, 2 patients with BPDCN (100%), and one of the 2 patients (50%) with other cutaneous dendritic cell neoplasms also demonstrated shared mutations between the skin and concurrent or subsequent myeloid neoplasms. Both BM and c-AML shared identical founding drivers, with a predominance of NPM1, DNMT3A, and translocations associated with monocytic differentiation, with common cutaneous-only mutations involving genes in the signal transduction and epigenetic pathways. Cutaneous histiocytic-dendritic neoplasms shared founding drivers in ASXL1, TET2, and/or SRSF2. However, in the Langerhans cell histiocytosis or histiocytic sarcoma cases, there exist recurrent secondary RAS pathway hits, whereas cutaneous BPDCN cases exhibit copy number or structural variants. These results enrich and broaden our understanding of clonally related cutaneous manifestations of myeloid neoplasms and further illuminate the highly diverse spectrum of morphologic and immunophenotypic features they exhibit.

Unicentric Castleman Disease: Illustration of Its Morphologic Spectrum and Review of the Differential Diagnosis

CONTEXT.—

Unicentric Castleman disease (UCD) is a dynamic entity with a wide spectrum of morphologic findings. UCD can be further subdivided into hyaline-vascular and mixed/plasmacytic variants. Hyaline-vascular UCD has both follicular and interfollicular (stromal) changes, and occasionally these lesions show a skewed representation of either the follicular or stromal compartments. Plasmacytosis is usually minimal in the hyaline-vascular variant. The mixed/plasmacytic variant of UCD is composed of sheets of plasma cells often associated with a variable number of follicles with regressive changes.

OBJECTIVE.—

To illustrate the differential diagnosis of UCD, as it is quite broad and includes lymphomas, plasma cell neoplasms, stromal neoplasms such as follicular dendritic cell sarcoma and vascular neoplasms, immunoglobulin G4-related disease, infections, and other rare lesions. An additional objective is to enhance awareness of the morphologic features of UCD in excisional and in small core-needle biopsy specimens, the latter of which may inadvertently target follicle- or stroma-rich areas, causing diagnostic challenges.

DATA SOURCES.—

In this review, we provide readers a concise illustration of the morphologic spectrum of UCD that we have encountered in our practice and a brief discussion of entities in the differential diagnosis.

CONCLUSIONS.—

UCD exhibits a broad spectrum of morphologic changes, and awareness of these morphologic variations is key to avoid misdiagnosis.

Monocytic and blastic plasmacytoid dendritic cell differentiation in acute leukemia with KMT2A rearrangement

Acute leukemia with KMT2A rearrangement shows a spectrum of immunophenotypic presentation, but blastic plasmacytoid dendritic cell differentiation is extremely rare. Here we present a case of KMT2A rearranged acute leukemia with a hybrid immunophenotype in which a single blast population showed both blastic plasmacytoid dendritic cell and monocytic differentiation. This unusual case contributes to the diversity of the immunophenotypic spectrum in KMT2A rearranged acute leukemia and also sheds light on the cell of origin of plasmacytoid dendritic cells.

Blastic Plasmacytoid Dendritic Cell Neoplasm: A Case Report

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an uncommon hematological tumor originating from the precursor of plasmacytoid dendritic cells (pDCs) with a persistent and progressive course of illness. Despite being an aggressive disease BPDCN has an initial indolent course manifested as skin lesions. Alongside or following the skin lesion, the extra-cutaneous manifestation develops and includes lymphadenopathy, splenomegaly, and hepatomegaly. The BPDCN diagnosis is mainly based on the immunophenotype.  Herein, we report the case of a 72-year-old male patient who presented with a history of left anterior chest wall painless skin lesions. Histology of skin biopsy of the left chest skin lesion showed diffuse dermal infiltration by monomorphic medium-sized blastic cells positive for cluster of differentiation (CD)4, CD45, CD7, CD56, CD43, CD123, T-cell leukemia-1 (TCL1), and B-cell leukemia/lymphoma 2 protein (BCL2). Given the rarity of the disease, standard chemotherapy regimens used in treating different leukemias and lymphomas have been adapted to treat BPDCN.

Early T-cell precursor lymphoblastic leukemia accompanied by prominent blastic plasmacytoid dendritic cell proliferation mimicking blastic plasmacytoid dendritic cell neoplasm: an exceptional case report and literature review

PURPOSE

Plasmacytoid dendritic cells (pDCs) are commonly associated with myeloid malignancies. The association between lymphoblastic leukemia and pDCs has been little explored.

CASE PRESENTATION

Here, we report a novel case of early T-cell precursor lymphoblastic leukemia (ETP-ALL) accompanied by prominent proliferation of blastic pDCs mimicking BPDCN. The diagnosis was established based on a comprehensive analysis of morphology, immunophenotype and clinical implications. We also present a literature review and discussion on the differential expression of reactive and neoplastic pDCs, the functional role of pDCs in lymphoblastic leukemia, and the etiological association of normal pDCs and BPDCN.

CONCLUSIONS

The current case demonstrates for the first time that prominent pDC proliferation can be associated with lymphoid neoplasms and can exhibit blastic morphology and immunophenotype. The underlying mechanism of the coexistence of these two blastic populations remains unknown. Further genetic profiling may be required to denote the progressive development of tumor stem cells to the lymphoid, myeloid or dendritic cell lineage. Moreover, the prognostic value of pDCs in hematological neoplasms needs further investigation.

Immunophenotypic and Molecular Features of Acute Myeloid Leukemia with Plasmacytoid Dendritic Cell Differentiation Are Distinct from Blastic Plasmacytoid Dendritic Cell Neoplasm

Acute myeloid leukemia (AML) with ≥2% plasmacytoid dendritic cells (pDC) has been recently described as AML with pDC differentiation (pDC-AML) characterized by pDC expansion with frequent RUNX1 mutations. In this study, we investigated a cohort of 53 pDC-AML cases representing about 3% of all AML cases. We characterized their immunophenotype and genetic profiles and compared these findings with blastic plasmacytoid dendritic cell neoplasm (BPDCN). pDC-differentiation/expansion was preferentially observed in AML with an immature myeloid or myelomonocytic immunophenotype, where myeloblasts were frequently positive for CD34 (98%), CD117 (94%), HLA-DR (100%) and TdT (79%), with increased CD123 (89%) expression. The median number of pDCs in pDC-AML was 6.6% (range, 2% to 26.3%) and their immunophenotype reminiscent of pDCs in early or intermediate stages of differentiation. The immunophenotype of pDCs in pDC-AML was different from BPDCN (n = 39), with major disparities in CD34 (96% vs. 0%), CD56 (8% vs. 97%) and TCL1 (12% vs. 98%) and significant differences in frequency of CD4, CD13, CD22, CD25, CD36, CD38, CD117 and CD303 expression. At the molecular level, the genetic landscapes of pDC-AML and BPDCN also differ, with RUNX1 mutations detected in 64% of pDC-AML versus 2% of BPDCN. Disparities in TET2 (21% vs. 56%), FLT3 (23% vs. 0%), DNMT3A (32% vs. 10%) and ZRSR2 (2% vs. 16%) (all p < 0.05) were also detected. The distinct immunophenotypic and mutation profiles of pDC-AML and BPDCN indicate that the neoplastic pDCs in pDC-AML and BPDCN derived from different subsets of pDC precursors.

A very rare case of FLT3-D835 positive blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasms (BPDCNs) are extremely rare and aggressive hematological malignancies that derive from precursors of plasmacytoid dendritic cells (pDC) and frequently involve skin lesions and bone marrow infiltration. They mostly affect the elderly population and the prognosis is poor with the therapeutic choices currently available. Diagnosis is made with the help of tools such as immunohistochemistry and flow cytometry. Here, we present a particular case of BPDCN with a positive FLT3-D835 mutation and we discuss the possible impact this may have on the evolution of the disease and response to treatment.

Blastic Plasmacytoid Dendritic Cell Neoplasm without Cutaneous Manifestation: A Case Report

Patient: Male, 85-year-old

Final Diagnosis: Blastic plasmacytoid dendritic cell neoplasm

Symptoms: Dizziness • leg pain • malaise • weakness

Medication: —

Clinical Procedure: Bone marrow biopsy • lumbar puncture

Specialty: Hematology • Oncology

Blastic Plasmacytoid Dendritic Cell Neoplasm: Progress in Cell Origin, Molecular Biology, Diagnostic Criteria and Therapeutic Approaches

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy characterized by recurrent skin nodules, an aggressive clinical course with rapid involvement of hematological organs, and a poor prognosis with poor overall survival. BPDCN is derived from plasmacytoid dendritic cells (pDCs) and its pathogenesis is unclear. The tumor cells show aberrant expression of CD4, CD56, interleukin-3 receptor alpha chain (CD123), blood dendritic cell antigen 2 (BDCA 2/CD303), blood dendritic cell antigen 4 (BDCA4) and transcription factor (E protein) E2-2 (TCF4). The best treatment drugs are based on experience by adopting those used for either leukemia or lymphoma. Relapse with drug resistance generally occurs quickly. Stem cell transplantation after the first complete remission is recommended and tagraxofusp is the first targeted therapy. In this review, we summarize the differentiation of BPDCN from its cell origin, its connection with normal pDCs, clinical characteristics, genetic mutations and advances in treatment of BPDCN. This review provides insights into the mechanisms of and new therapeutic approaches for BPDCN.

Transcriptomic and genomic heterogeneity in blastic plasmacytoid dendritic cell neoplasms: from ontogeny to oncogenesis

Oncogenesis and ontogeny of blastic plasmacytoid dendritic cell neoplasm (BPDCN) remain uncertain, between canonical plasmacytoid dendritic cells (pDCs) and AXL+ SIGLEC6+ DCs (AS-DCs). We compared 12 BPDCN to 164 acute leukemia by Affymetrix HG-U133 Plus 2.0 arrays: BPDCN were closer to B-cell acute lymphoblastic leukemia (ALL), with enrichment in pDC, B-cell signatures, vesicular transport, deubiquitination pathways, and AS-DC signatures, but only in some cases. Importantly, 1 T-cell ALL clustered with BPDCN, with compatible morphology, immunophenotype (cCD3+ sCD3- CD123+ cTCL1+ CD304+), and genetics. Many oncogenetic pathways are deregulated in BPDCN compared with normal pDC, such as cell-cycle kinases, and importantly, the transcription factor SOX4, involved in B ontogeny, pDC ontogeny, and cancer cell invasion. High-throughput sequencing (HaloPlex) showed myeloid mutations (TET2, 62%; ASXL1, 46%; ZRSR2, 31%) associated with lymphoid mutations (IKZF1), whereas single-nucleotide polymorphism (SNP) array (Affymetrix SNP array 6.0) revealed frequent losses (mean: 9 per patient) involving key hematological oncogenes (RB1, IKZF1/2/3, ETV6, NR3C1, CDKN2A/B, TP53) and immune response genes (IFNGR, TGFB, CLEC4C, IFNA cluster). Various markers suggest an AS-DC origin, but not in all patients, and some of these abnormalities are related to the leukemogenesis process, such as the 9p deletion, leading to decreased expression of genes encoding type I interferons. In addition, the AS-DC profile is only found in a subgroup of patients. Overall, the cellular ontogenic origin of BPDCN remains to be characterized, and these results highlight the heterogeneity of BPDCN, with a risk of a diagnostic trap.

Blastic Plasmacytoid Dendritic Cell Neoplasm: Clinical Presentation and Diagnosis

Clinical and biological presentation of patients with blastic plasmacytoid dendritic cell neoplasm (BPDCN) is depicted to highlight criteria that might alert physicians. Diagnosis of BPDCN is still challenging and requires (1) immunophenotyping of blood or bone marrow aspiration using several markers (CD4, CD56, HLA-DR, myeloid and lymphoid lineage markers) and should include pDC markers such as CD123, cTCL1, CD303, and CD304, and/or (2) pathologic analysis of cutaneous lesions, also with immunohistochemistry using markers specific to BPDCN.

Molecular Features of Blastic Plasmacytoid Dendritic Cell Neoplasm: DNA Mutations and Epigenetics

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic neoplasm with a dismal prognosis and no standard therapy. In the past, its cellular ontogenesis was obscure, and BPDCN had been erroneously named CD56⁺/TdT⁺ blastic NK cell tumor and CD4⁺/CD56⁺ hematodermic neoplasm. Finally, in 2008, the BPDCN was correctly recognized as a neoplasm deriving from the malignant transformation of plasmacytoid dendritic cell precursors and classified among the myeloid neoplasms. Since then, the understanding of BPDCN biology has improved rapidly: the DNA mutational status of BPDCN has been extensively investigated revealing a spectrum perfectly resembling its myeloid lineage derivation.

Myeloid Neoplasms with Elevated Plasmacytoid Dendritic Cell Differentiation Reflect the Maturation Process of Dendritic Cells

To date, the research on dendritic cells (DCs) and their correlated neoplasms has not been clear. Blastic plasmacytoid dendritic cell neoplasm (BPDCN) and mature plasmacytoid dendritic cell proliferation (MPDCP) are two types of malignancies originating from plasmacytoid dendritic cells (pDCs). Some evidence has indicated the existence of other pDC neoplasms. In addition, cases of myeloid neoplasms (MNs), acute myeloblastic leukemia (AML), and myelodysplastic syndrome (MDS) with increased pDCs (AML/MDS-pDCs) seem to have immature DCs according to the vaguely consistent expression of markers among MNs and pDCs, which appear to fit the developmental pattern of normal DCs. We analyzed 14 AML/MDS-pDC cases mainly for their immunophenotype by flow cytometry and inferred their CD expression pattern. The patients' clinical information and other laboratory data were collected and reviewed. AML/MDS-pDCs show a different pattern of markers from BPDCN and MPDCP. Three maturation-involved stages were found in these AML/MDS-pDCs patients. Stage I was the most immature stage and displayed an expression profile of CD34^+/st+ CD117^+/st+ BDCA2^- BDCA4^- CD123⁺ HLA-DR^+/st+ CD4^- CD45dim⁺ ; Stage II was the more immature stage displayed a phenotype of CD34^dim+ CD117^dim+ BDCA2^-/dim+ BDCA4^-/dim+ CD123^st+ HLA-DR^+/st+ CD4^- CD45⁺ ; and Stage III was the mature stage showed CD34^- CD117^- BDCA2⁺ /BDCA4⁺ CD123^st+ HLA-DR^+/st+ CD4⁺ CD45^+/st+ . Three maturation-involved stages overlapped well with the phenotypes of normal DC progenitors in a continuously developmental process: granulocyte, monocyte, and DC progenitors (GMDPs) and/or monocyte and DC progenitors (MDPs), common DC progenitors (CDPs), pDCs, and/or pre-DCs. In this study, we considered AML/MDS-pDCs as entities that were distinct from BPDCN and MPDCP and correlated the components of this tumor with the normal DC differentiation pathway, which provides new evidence for understanding DC neoplasms. © 2019 International Society for Advancement of Cytometry.

PD1/PD-L1 Expression in Blastic Plasmacytoid Dendritic Cell Neoplasm

Patients with blastic plasmacytoid dendritic cell neoplasm (BPDCN) have poor outcomes despite intensive chemotherapy, underscoring the need for novel therapeutic approaches. The expression status of PD1/PD-L1 in BPDCN remains unknown. We evaluated PD1/PD-L1 by immunohistochemistry and RNAseq expression profiling in a cohort of BPDCN patients. The study group included 28 patients with a median age of 66.8 years (range, 22.8–86.7), 22 men and 6 women. PD-L1 expression was detected by immunohistochemistry in 10/21 (47.6%) cases. PD-L1 expression had a median H-score of 157. The H-score was ≥60 in 7 patients. PD-L1 protein levels (H-score) were proportional to normalized PD-L1 mRNA transcript levels (CD274 mRNA). In addition, high-level PD-L1 expression correlated with higher numbers of PD1-positive cells within BPDCN tumors. There was no correlation between clinicopathologic characteristics and PD-L1 expression status. Similarly, there was no significant difference in overall survival between patients with PD-L1-positive and PD-L1-negative BPDCN (median 12 vs. 23 month, respectively; p = 0.743). In conclusion, PD-L1 expression by tumor cells is detectable in a sizeable subset of patients with BPDCN, suggesting that exploration of the effectiveness of therapeutic inhibition of the PD1/PD-L1 axis in patients with refractory or progressive BPDCN is warranted.

Genomic aberrations involving 12p/ETV6 are highly prevalent in blastic plasmacytoid dendritic cell neoplasms and might represent early clonal events

BACKGROUND

Chromosomal aberrations at the ETV6 gene locus on 12p13.2 are common in bone marrow samples involved by blastic plasmacytoid dendritic cell neoplasm (BPDCN). However, their pathogenic role, incidence in cutaneous BPDCN lesions, and clinical significance have not been assessed systematically.

RESULTS

The study group included 30 BPDCN patients, 25 men and 5 women, with a median age of 64 years. Conventional cytogenetic analysis demonstrated karyotypic aberrancies in 15 cases, of which 8 had chromosomal lesions involving 12p. In addition, 2 cases with normal diploid karyotype had cryptic 12p/ETV6 deletion by ETV6 FISH test. Notably, 2 bone marrow samples with ETV6 rearrangement had no detectable BPDCN involvement, but otherwise dynamic changes in the detection of 12p/ETV6 aberrations correlated with the presence of morphologically and/or immunophenotypically detectable disease. Tissue specimens from 6 patients with cutaneous BPDCN all tested positive for homozygous or heterozygous ETV6 deletions.

CONCLUSION

We demonstrate that monoallelic and biallelic 12p/ETV6 deletions are highly prevalent in BPDCN, and their detection is enhanced by the use of FISH and aCGH. In addition, 12p/ETV6 may be present in the bone marrow of BPDCN patients in the absence of detectable disease suggesting that such alterations might represent an early pathogenic event.

Treatment of blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare myeloid malignancy with no defined standard of care. BPDCN presents most commonly with skin lesions with or without extramedullary organ involvement before leukemic dissemination. As a result of its clinical ambiguity, differentiating BPDCN from benign skin lesions or those of acute myeloid leukemia with leukemia cutis is challenging. BPDCN is most easily defined by the phenotype CD4⁺CD56⁺CD123⁺lineage^-MPO^-, although many patients will present with variable expression of CD4, CD56, or alternate plasmacytoid markers, which compounds the difficulty in differentiating BPDCN from other myeloid or lymphoid malignancies. Chromosomal aberrations are frequent, and the mutational landscape of BPDCN is being rapidly characterized although no obvious molecular target for chemoimmunotherapy has been identified. Chemotherapy regimens developed for acute myeloid leukemia, acute lymphoid leukemia, and myelodysplastic syndrome have all been used to treat BPDCN. Relapse is frequent, and overall survival is quite poor. Allogeneic transplantation offers a chance at prolonged remission and possible cure for those who are eligible; unfortunately, relapse remains high ranging from 30% to 40%. Novel therapies such as SL-401, a diphtheria toxin conjugated to interleukin-3 (IL-3) is commonly overexpressed in BPDCN and other aggressive myeloid malignancies and has shown considerable promise in ongoing clinical trials. Future work with SL-401 will define its place in treating relapsed or refractory disease as well as its role as a first-line therapy or bridge to transplantation.

Simultaneous deletion of 3'ETV6 and 5'EWSR1 genes in blastic plasmacytoid dendritic cell neoplasm: case report and literature review

Background

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic malignancy. Based on literature reports of limited cases, over 50 % of BPDCN have chromosomal abnormalities, but no single chromosomal change has been identified as diagnostic of this entity.

Case presentation

In this report, we present a case of BPDCN with complicated chromosomal abnormalities involving chromosomes 12 and 22 and resulting in a simultaneous partial deletion of ETV6 and EWSR1. Notably, these aberrations were identified in bone marrow myeloid precursors in the absence of bone marrow involvement by BPDCN.

Conclusion

Analysis of 46 BPDCN cases with abnormal karyotypes (45 from literature reports plus this case) showed that 12p- is one of the most common structural aberrations in BPDCN. The ETV6 and CDKN1B on 12p deserve further investigations as potential markers of BPDCN.

Neoplasms derived from plasmacytoid dendritic cells

Plasmacytoid dendritic cell neoplasms manifest in two clinically and pathologically distinct forms. The first variant is represented by nodular aggregates of clonally expanded plasmacytoid dendritic cells found in lymph nodes, skin, and bone marrow ('Mature plasmacytoid dendritic cells proliferation associated with myeloid neoplasms'). This entity is rare, although likely underestimated in incidence, and affects predominantly males. Almost invariably, it is associated with a myeloid neoplasm such as chronic myelomonocytic leukemia or other myeloid proliferations with monocytic differentiation. The concurrent myeloid neoplasm dominates the clinical pictures and guides treatment. The prognosis is usually dismal, but reflects the evolution of the associated myeloid leukemia rather than progressive expansion of plasmacytoid dendritic cells. A second form of plasmacytoid dendritic cells tumor has been recently reported and described as 'blastic plasmacytoid dendritic cell neoplasm'. In this tumor, which is characterized by a distinctive cutaneous and bone marrow tropism, proliferating cells derive from immediate CD4(+)CD56(+) precursors of plasmacytoid dendritic cells. The diagnosis of this form can be easily accomplished by immunohistochemistry, using a panel of plasmacytoid dendritic cells markers. The clinical course of blastic plasmacytoid dendritic cell neoplasm is characterized by a rapid progression to systemic disease via hematogenous dissemination. The genomic landscape of this entity is currently under intense investigation. Recurrent somatic mutations have been uncovered in different genes, a finding that may open important perspectives for precision medicine also for this rare, but highly aggressive leukemia.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN): a rare entity

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive haematological malignancy in the elderly, with a high frequency of cutaneous and bone marrow involvement and poor prognosis. We report a case of BPDCN with classic presentation and discuss its treatment and the value of different investigation tools used in diagnosis and response assessment.

Extramedullary Manifestations of Myeloid Neoplasms

OBJECTIVES

This session of the 2013 Society of Hematopathology/European Association for Haematopathology workshop focused on extramedullary manifestations of myeloid neoplasms.

METHODS

We divided the submitted cases into four subgroups: (1) isolated myeloid sarcoma (MS); (2) MS with concurrent acute myeloid leukemia (AML), with a focus on karyotypic and molecular findings; (3) extramedullary relapse of AML, including relapse in the posttransplant setting; and (4) blast phase/transformation of a myeloproliferative neoplasm or chronic myelomonocytic leukemia.

RESULTS

Establishing a diagnosis of isolated MS requires a high index of suspicion and use of immunophenotypic methods. Recurrent cytogenetic abnormalities or gene mutations that occur in MS mirror those known to occur in AML.

CONCLUSIONS

In the era of targeted therapy and sophisticated risk stratification, every attempt must be made to perform a complete workup on MS cases (or concurrent AML) since the diagnosis of MS, in itself, is no longer adequate for patient management. Cases of blastic plasmacytoid dendritic cell neoplasm were also included and discussed in this session.

Blastic plasmacytoid dendritic cell neoplasm: update on molecular biology, diagnosis, and therapy

BACKGROUND

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy with an aggressive clinical course. Most patients with BPDCN have skin lesions and simultaneous involvement of the peripheral blood, bone marrow, and lymph nodes.

METHODS

A search of PubMed and Medline was conducted for English-written articles relating to BPDCN, CD4(+)CD56(+) hematodermic neoplasm, and blastic natural killer cell lymphoma. Data regarding diagnosis, prognosis, and treatment were analyzed.

RESULTS

BPDCN is derived from precursor plasmacytoid dendritic cells. The diagnosis of BPDCN is based on the characteristic cytology and immunophenotype of malignant cells coexpressing CD4, CD56, CD123, blood dendritic cell antigens 2 and 4, and CD2AP markers. Multiple chromosomal abnormalities and gene mutations previously reported in patients with myeloid and selected lymphoid neoplasms were identified in approximately 60% of patients with BPDCN. Prospectively controlled studies to guide treatment decisions are lacking. The overall response rate with aggressive acute lymphoblastic leukemia-type induction regimens was as high as 90%, but the durability of response was short. Median survival rates ranged between 12 and 16 months. Patients with relapsed disease may respond to L-asparaginase-containing regimens. Allogeneic hematopoietic stem cell transplantation, particularly when performed during the first remission, may produce durable remissions in selected adults.

CONCLUSIONS

BPDCN is a rare aggressive disease that typically affects elderly patients. The most commonly affected nonhematopoietic organ is the skin. Although BPDCN is initially sensitive to conventional chemotherapy regimens, this response is relatively short and long-term prognosis is poor. In the near future, novel targeted therapies may improve outcomes for patients with BPDCN.

CD4+ CD56+ Hematodermic Neoplasm Without Cutaneous Involvement

CD4+/CD56+ hematodermic neoplasm is a recently recognized highly aggressive tumor presenting in skin, usually with lymph node and bone marrow involvement, often terminating in a leukemic phase. It has a distinct clinical presentation of primary skin lesions in the form of papules, nodules or bruise like areas. Bone marrow and peripheral blood involvement without skin involvement is a very rare phenomenon. We are reporting an interesting case where an elderly male, a known diabetic, when investigated for the cause of generalised weakness was found to have CD4+/CD56+ hematodermic neoplasm, the unusual feature being absence of any associated cutaneous involvement.

TET2 mutations, myelodysplastic features, and a distinct immunoprofile characterize blastic plasmacytoid dendritic cell neoplasm in the bone marrow

Distinguishing blastic plasmacytoid dendritic cell neoplasm (BPDCN) from acute myeloid leukemia (AML) is gaining increased importance because of emerging differences in therapeutic approaches, and this distinction can be problematic in bone marrow specimens. We identified retrospectively 16 patients with bone marrow involvement by BPDCN: 11 men and 5 women with a median age of 62.5 years (range, 19-86 years). Myelodysplastic changes were observed in five patients. Immunophenotypic analysis showed that the neoplastic cells were positive for CD4, CD123, TCL-1, and HLA-DR and were negative for CD3, CD8, CD13, CD19, CD34, and myeloperoxidase. Other antigens expressed by subsets of BPDCN cases included the following: CD56 (13/15; 81%), CD33 (7/10; 70%), CD7 (11/14; 69%), TdT (5/15; 33%), CD2 (5/11; 31%), CD117 (2/9; 22%), and CD5 (2/13; 15%). Conventional cytogenetic analysis showed chromosomal abnormalities in 6 of 13 (46%) cases analyzed, of which 3 cases had -13/13q-. Targeted next-generation sequencing performed on five BPDCN cases identified TET2 (ten eleven translocation 2) mutations and no other AML-associated mutations. In conclusion, BPDCN in the bone marrow has a characteristic immunoprofile (CD4+, CD56+, CD123+, and TCL-1+) and appears to be commonly associated with myelodysplastic features and a high frequency of TET2 mutations in the absence of other mutations commonly observed in AML.

Specific skin lesions in chronic myelomonocytic leukemia: a spectrum of myelomonocytic and dendritic cell proliferations: a study of 42 cases

Chronic myelomonocytic leukemia (CMML) is a rare clonal hematopoietic disorder that can also involve the skin. The histopathology of these skin lesions is not clearly defined, and few data are available in the literature. To better understand tumoral skin involvements in CMML we carried out an extensive, retrospective clinicopathologic study of 42 cases selected from the database of the French Study Group of Cutaneous Lymphomas. On the basis of clinical data, morphology, and phenotype we identified 4 clinicopathologic profiles representing 4 distinct groups. The first group comprised myelomonocytic cell tumors (n=18), exhibiting a proliferation of granulocytic or monocytic blast cells, which were CD68 and/or MPO positive but negative for dendritic cell markers. The second group comprised mature plasmacytoid dendritic cell tumors (n=16), denoted by a proliferation of mature plasmacytoid dendritic cells, which were CD123, TCL1, and CD303 positive but CD56, CD1a, and S100 negative. The third group comprised blastic plasmacytoid dendritic cell tumors (n=4), characterized by a proliferation of monomorphous medium-sized blast cells, which were CD4, CD56, CD123, TCL1 positive but CD1a and S100 negative. The fourth group consisted of a putatively novel category of tumor that we named blastic indeterminate dendritic cell tumors (n=4), distinguished by a proliferation of large blast cells that not only exhibited monocytic markers but also the dendritic markers CD1a and S100. These 4 groups showed distinctive outcomes. Finally, we showed, by fluorescence in situ hybridization analysis, a clonal link between bone marrow disease and skin lesions in 4 patients. Herein, we have described a novel scheme for pathologists and physicians to handle specific lesions in CMML, which correspond to a spectrum of myelomonocytic and dendritic cell proliferations with different outcomes. A minimal panel of immunohistochemical markers including CD68, CD1a, S100, Langerin, and CD123 is necessary to make the correct classification in this spectrum of cutaneous CMML tumors, in which dendritic cell lineage plays an important role.

Immunophenotypic analysis of myeloperoxidase-negative leukemia cutis and blastic plasmacytoid dendritic cell neoplasm

Myeloid leukemia cutis (LC) and blastic plasmacytoid dendritic cell neoplasm (BPDCN) are morphologically indistinguishable malignancies that frequently manifest in the skin. Separating myeloperoxidase-negative LC from BPDCN may be particularly challenging. We identified a panel of immunohistochemical stains to distinguish myeloid LC (23 cases) from BPDCN (12 cases): myeloperoxidase, which stained 7 cases (30%) of LC and 0 cases (0%) of BPDCN; CD56, which stained 12 cases (52%) of LC and all 12 cases (100%) of BPDCN; CD4, which stained 2 cases (9%) of LC and all 12 cases (100%) of BPDCN; CD123, which stained 4 cases (17%) of LC and 10 cases (83%) of BPDCN; and Tcl-1, which stained 2 cases (9%) of LC and 9 (82%) of 11 cases of BPDCN. It is interesting that CD33 was not helpful; it stained 18 (78%) cases of LC and 11 cases (92%) of BPDCN. Our results indicate that a panel that includes CD4, CD56, CD123, and Tcl-1 can appropriately distinguish between these 2 entities.

Histologic and immunohistologic characterization of skin localization of myeloid disorders: a study of 173 cases

A retrospective analysis of 173 skin biopsy specimens of myeloid leukemia cutis (MLC) was performed to determine histologic and immunophenotypic criteria that could distinguish the varied myeloid disorders from one another. For the study, 11 relevant histologic items were scored and 12 antigens were studied (CD68 [KP1], CD163, CD14, CD4, myeloperoxidase [MPO], CD33, CD117, CD34, CD56, MIB-1, CD303, and CD123). Underlying myeloid disorders were essentially acute myeloid leukemias (65.3%), chronic myelomonocytic leukemias (11.0%), and refractory anemia (10.4%). Skin lesions were de novo in 7.5%, concurrent in 26.6%, and subsequent in 60.7%. Several morphologic characteristics (density, size of tumor cells, inflammatory background) were statistically useful in distinguishing between varied myeloid disorders. De novo MLCs displayed a specific morphologic profile. Association of CD68, CD33, and MPO could diagnose 100% of the cases of MLC. However, the immunohistochemical panel could not distinguish between the varied underlying myeloid disorders, with the exception that CD123 was particularly powerful in recognizing chronic myelomonocytic leukemia and also permitted reclassification of 4 cases as blastic plasmacytoid dendritic cell neoplasm.

Blastic plasmacytoid dendritic cell neoplasm expressing the CD13 myeloid antigen

Blastic plasmacytoid dendritic cell neoplasm (BPDCN), currently considered to originate from immature plasmacytoid dendritic cells (DC), is a rare and aggressive CD4+CD56+ neoplasm that frequently involves the skin and bone marrow. We present a case of an 80-year-old man with a CD4+CD56+ BPDCN that affected the orbital cavity and bone marrow. Although BPDCN has not been reported to express any lineage-specific markers, the neoplastic cells strongly expressed the CD13 antigen. Therefore, in addition to pathological examination, we attempted to induce in vitro morphological and surface marker changes with IL-3 and CD40 ligand. After treatment with these cytokines, the tumor cells enlarged markedly, acquired many fine dendrites, similar to mature DC, and showed enhanced expression of antigens specific to DC or antigen-presenting cells, such as CD40, CD80, CD83 and CD86. To the best of our knowledge, this is the first report of BPDCN expressing a myeloid antigen, CD13, although CD33 expression has been described in some cases. The present patient received 2 courses of combination chemotherapy consisting of cytarabine and etoposide, which resulted in complete remission. Given that the cellular origin of plasmacytoid DC is still controversial, myeloid antigen expression involving CD13 may not exclude a diagnosis of BPDCN.

Histiocytic and Dendritic Cell Neoplasms

This article reviews the features of dendritic cells (DCs) of myeloid-derived, plasmacytoid, and follicle-associated types and tumors of these cells, as well as myeloid sarcoma. The morphologic and immunophenotypic features in this group of neoplasms is featured, including mature neoplasms such as Langerhans cell histiocytosis, its malignant counterpart Langerhans cell sarcoma, and S100-negative histiocytic proliferations. More immature or precursor malignancies in this group include myeloid and monocytic leukemias presenting in extramedullary tissues as well as the newly codified blastic plasmacytoid dendritic cell neoplasm. Although likely not related histogenetically to myeloid-derived DCs, mesenchymal-type lymph node tumors including follicular dendritic cell and fibroblastic reticulum sarcomas are also discussed. All of these neoplasms can exhibit a range of immunophenotypic and morphologic features that underscore the plasticity of the non-neoplastic precursors from which they are derived.

CD4-/CD56+/CD123+ Hematodermic Neoplasm Showing Early Liver Metastasis

Hematodermic neoplasm (HN) is a clinically aggressive neoplasm with a high incidence of cutaneous involvement and a risk of leukemic dissemination. In the recent WHO-EORTC classification, the term blastic natural killer cell lymphoma has been replaced with CD4+/CD56+ HN because of its derivation from a plasmacytoid dendritic cell precursor. Cases of HN that completely lack CD4 or CD56 expression, therefore represents a diagnostic problem. A 68-year-old Korean male was diagnosed with CD4-/CD56+ HN and treated with hyper-CVAD (cyclophosphamide, vincristine, doxorubicin, dexamethasone) at initial treatment, and then switched to high dose methotrexate/cytarabine. His disease relapsed and resulted in death from bone and brain disease 6 months after complete clinical remission, despite diagnostic workups, including a radioisotope liver scan and ultrasound-guided fine needle aspiration biopsy. Further cytogenetic studies such as comparative genomic hybridization could elucidate the genetic mechanisms in the development and progression of lymphomas. We report an unusual case of 'CD4-/CD56+/CD123+ HN' showing early liver metastasis.

Immunocytochemistry and the diagnosis of cutaneous lymphoma

Cutaneous lymphoid infiltrates may pose some of the most difficult diagnostic problems in dermatopathology. Immunocytochemistry is often employed in an effort to determine whether an infiltrate is neoplastic or, in the case of clearly malignant infiltrates, to provide a specific diagnosis. The rarity of these disorders and the variant immunocytochemical profiles they may present further thwart understanding and sometimes prevent an accurate diagnosis. In this review the common immunocytochemical profiles of various cutaneous lymphomas are presented and potential pitfalls and problems considered. Immunocytochemistry is not a diagnostic test but, as in other areas of histopathology, is a highly valuable tool that requires critical interpretation within a context: so applied, it is an indispensable part of the pathologist's arsenal in evaluating lymphoid infiltrates and defining different lymphomas.