Recurrent 8q24 rearrangement in blastic plasmacytoid dendritic cell neoplasm: association with immunoblastoid cytomorphology, MYC expression, and drug response

Multicenter analysis of outcomes in blastic plasmacytoid dendritic cell neoplasm offers a pretargeted therapy benchmark

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an uncommon hematologic malignancy with poor outcomes. Existing data on the clinical behavior of BPDCN are limited because reported outcomes are from small retrospective series, and standardized treatment guidelines are lacking. The interleukin-3 cytotoxin conjugate tagraxofusp was recently tested in phase 1/2 trials that led to US Food and Drug Administration approval, the first ever for BPDCN. However, because there was no matched internal comparator in this or any clinical study to date, results of BPDCN trials testing new drugs are difficult to compare with alternative therapies. We therefore sought to define the clinical characteristics and outcomes of a group of patients with BPDCN treated at 3 US cancer centers in the modern era but before tagraxofusp was available. In 59 studied patients with BPDCN, the median overall survival from diagnosis was 24 months, and outcomes were similar in patients with "skin only" or with systemic disease at presentation. Intensive first-line therapy and "lymphoid-type" chemotherapy regimens were associated with better outcomes. Only 55% of patients received intensive chemotherapy, and 42% of patients underwent stem cell transplantation. Clinical characteristics at diagnosis associated with poorer outcomes included age >60 years, abnormal karyotype, and terminal deoxynucleotidyltransferase (TdT) negativity in the BPDCN cells. We also identified disease responses to pralatrexate and enasidenib in some patients. This study highlights poor outcomes for patients with BPDCN in the modern era and the need for new treatments. Outcomes from ongoing clinical trials for BPDCN can be evaluated relative to this contemporary cohort.

Successful outcome of second allogeneic bone marrow transplantation for blastic plasmacytoid dendritic cell neoplasm with MYC locus rearrangement

A 62-year-old male was diagnosed with blastic plasmacytoid dendritic cell neoplasm (BPDCN) with a MYC rearrangement. Four months after the first unrelated bone marrow transplantation (BMT), he developed the relapsed BPDCN. After the achievement of partial remission following re-induction therapy, he underwent a second BMT from another unrelated donor, and experienced complete remission with grade II acute graft-versus-host disease and moderate chronic graft-versus-host disease. He remains alive in complete remission more than 71 months after the second BMT. These results suggested that donor change at the second transplantation may represent a considerable therapeutic option for patients with relapsed BPDCN.

Blastic Plasmacytoid Dendritic Cell Neoplasm: State of the Art and Prospects

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an extremely rare tumour, which usually affects elderly males and presents in the skin with frequent involvement of the bone-marrow, peripheral blood and lymph nodes. It has a dismal prognosis, with most patients dying within one year when treated by conventional chemotherapies. The diagnosis is challenging, since neoplastic cells can resemble lymphoblasts or small immunoblasts, and require the use of a large panel of antibodies, including those against CD4, CD56, CD123, CD303, TCL1, and TCF4. The morphologic and in part phenotypic ambiguity explains the uncertainties as to the histogenesis of the neoplasm that led to the use of various denominations. Recently, a series of molecular studies based on karyotyping, gene expression profiling, and next generation sequencing, have largely unveiled the pathobiology of the tumour and proposed the potentially beneficial use of new drugs. The latter include SL-401, anti-CD123 immunotherapies, venetoclax, BET-inhibitors, and demethylating agents. The epidemiologic, clinical, diagnostic, molecular, and therapeutic features of BPDCN are thoroughly revised in order to contribute to an up-to-date approach to this tumour that has remained an orphan disease for too long.

Lineage-specific RUNX2 super-enhancer activates MYC and promotes the development of blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive subtype of acute leukemia, the cell of origin of which is considered to be precursors of plasmacytoid dendritic cells (pDCs). Since translocation (6;8)(p21;q24) is a recurrent anomaly for BPDCN, we demonstrate that a pDC-specific super-enhancer of RUNX2 is associated with the MYC promoter due to t(6;8). RUNX2 ensures the expression of pDC-signature genes in leukemic cells, but also confers survival and proliferative properties in BPDCN cells. Furthermore, the pDC-specific RUNX2 super-enhancer is hijacked to activate MYC in addition to RUNX2 expression, thereby promoting the proliferation of BPDCN. We also demonstrate that the transduction of MYC and RUNX2 is sufficient to initiate the transformation of BPDCN in mice lacking Tet2 and Tp53, providing a model that accurately recapitulates the aggressive human disease and gives an insight into the molecular mechanisms underlying the pathogenesis of BPDCN.

Therapeutic Approaches for Blastic Plasmacytoid Dendritic Cell Neoplasm: Allogeneic Hematopoietic Cell Transplantation and Novel Therapies

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a clinically aggressive hematologic malignancy derived from precursors of plasmacytoid dendritic cells. There is no established standard therapy for BPDCN and the efficacy of conventional chemotherapy is limited, with an anticipated median overall survival ranging from 8 to 14 months. No randomized controlled trials have ever been performed to evaluate the benefit of frontline consolidation with an allogeneic hematopoietic cell transplant (allo-HCT) in BPDCN. Yet, offering an allograft has become the de facto option in BPDCN, and remains the only known long-term curative option for these patients, even in the modern era of targeted therapies. In our opinion, allo-HCT is recommended as part of frontline consolidation, especially in patients achieving first complete remission and who are deemed capable of tolerating the procedure, as published data show 3- to 4-year progression-free survival ranging from 69% to 74% in this population. Prompt referral to a transplant center, at the time of a diagnosis of BPDCN, is important to confirm allo-HCT candidacy and to initiate the process of identifying a suitable human leukocyte antigen (HLA)-compatible donor. Because disease relapse remains a major concern, additional strategies, such as post-allograft consolidation/maintenance therapy, are certainly needed to help further improve outcomes. Finally, patients deemed ineligible to receive an allo-HCT, due to lack of response and/or poor performance status, should be considered for enrollment in clinical trials.