Blastic plasmacytoid dendritic cell neoplasm with unusual lymphoid features and macrovacuoles

A 31-year-old male with a plasmacytoid dendritic blast cell neoplasm

Plasmacytoid blast dendritic cell neoplasm is a rare subtype of acute leukaemia that represents less than 1% of haematologic neoplasms. It is characterised by skin involvement and leukaemic dissemination in the rest of the body. The immunophenotype is represented by the expression of CD4, CD56 and CD123. Due to its low incidence, there is no standardised treatment. For most authors, acute lymphoblastic leukaemia) regimens with or without consolidation with allogeneic transplantation seem to be the most appropriate. We present the case of a 31-year-old male with a history of von Willebrand's disease, who was diagnosed with plasmacytoid blast dendritic cell neoplasm with central nervous system involvement. After receiving first-line immunopolychemotherapy with rituximab, the patient achieved complete haematologic remission with the high-dose ara-C regimen. Subsequently, he consolidated with allogeneic haploidentical transplantation.

Immunophenotypic characterization of reactive and neoplastic plasmacytoid dendritic cells permits establishment of a 10-color flow cytometric panel for initial workup and residual disease evaluation of blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematopoietic neoplasm whose immunophenotype remains incompletely characterized, particularly with regards to its distinction from reactive plasmacytoid dendritic cells (PDC). This limitation complicates detection of low-level involvement by BPDCN as well as minimal residual disease (MRD) assessment following therapy. We conducted the current study to characterize the immunophenotype of BPDCN in a cohort of 39 patients, and compared it to that of reactive PDC. We found that, in addition to CD56 expression (97%), BPDCN showed a number of aberrancies, including decreased/negative CD38 (82%), positive CD7 (64%), negative CD2 (81%), negative CD303 (56%), increased HLA-DR (69%) and decreased CD123 (78%) expression. Although BPDCN cells were characterized by CD56 expression, reactive PDC consistently included a CD56⁺ subset, ranging from 1.3%-20% (median 4.5%) of all PDC, challenging the detection of MRD. These CD56⁺ reactive PDC were, however, consistently positive for CD2 and CD303, brightly positive for CD38, and negative for CD7, distinctively different from BPDCN. Based on these findings, we set up a ten-color flow cytometry assay for BPDCN and validated it to a sensitivity of 0.01%. This panel was prospectively tested in 19 bone marrow samples from seven patients with BPDCN, and it effectively distinguished BPDCN cells from background reactive PDC in all cases. In summary, by understanding the immunophenotype of reactive and neoplastic PDC, BPDCN can be effectively detected by flow cytometry to a very low level using a panel of markers in addition to CD56. Such an assay could be used for initial bone marrow workup as well as MRD detection after therapy.

How should we diagnose and treat blastic plasmacytoid dendritic cell neoplasm patients?

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive leukemia for which we developed a nationwide network to collect data from new cases diagnosed in France. In a retrospective, observational study of 86 patients (2000-2013), we described clinical and biological data focusing on morphologies and immunophenotype. We found expression of markers associated with plasmacytoid dendritic cell origin (HLA-DRhigh, CD303+, CD304+, and cTCL1+) plus CD4 and CD56 and frequent expression of isolated markers from the myeloid, B-, and T-lymphoid lineages, whereas specific markers (myeloperoxidase, CD14, cCD3, CD19, and cCD22) were not expressed. Fifty-one percent of cytogenetic abnormalities impact chromosomes 13, 12, 9, and 15. Myelemia was associated with an adverse prognosis. We categorized chemotherapeutic regimens into 5 groups: acute myeloid leukemia (AML)-like, acute lymphoid leukemia (ALL)-like, lymphoma (cyclophosphamide, doxorubicin, vincristine, and prednisone [CHOP])-like, high-dose methotrexate with asparaginase (Aspa-MTX) chemotherapies, and not otherwise specified (NOS) treatments. Thirty patients received allogeneic hematopoietic cell transplantation (allo-HCT), and 4 patients received autologous hematopoietic cell transplantation. There was no difference in survival between patients receiving AML-like, ALL-like, or Aspa-MTX regimens; survival was longer in patients who received AML-like, ALL-like, or Aspa-MTX regimens than in those who received CHOP-like regimens or NOS. Eleven patients are in persistent complete remission after allo-HCT with a median survival of 49 months vs 8 for other patients. Our series confirms a high response rate with a lower toxicity profile with the Aspa-MTX regimen, offering the best chance of access to hematopoietic cell transplantation and a possible cure.