A category of rare and aggressive haematologic tumors co-expressing CD4 and CD56 antigens in the absence of any specific myeloid, B-, T-lymphoid or natural killer (NK) lineage markers is classified as blastic plasmacytoid dendritic cell neoplasms (BPDCN) according to the most recent 2008 WHO classification of tumours of haematopoietic and lymphoid tissues (1). This is in line with the recent knowledge that BPDCN are derived from the precursors of plasmacytoid dentritic cells (2-4). However, in the past a number of different terms were used for BPDCN due to their uncommon immunophenotypic, histopathological and clinical features, including blastic NK leukemia/lymphoma, histiocytic lymphoma or histiocytic associated hematologic malignancy, cutaneous a granular CD4+ CD56+ hematodermic neoplasm and NK-cell lymphoma or myelo-monocytic precursor – related lymphoma (5-12).

BPDCN are diagnosed about three times more often among men than women, mainly in the elderly (median age at diagnosis at 7th decade of live) (5, 10). Till present the etiology of BPDCN has not been elucidated. Epstein Barr virus and HIV had been previously supposed to play a role in BPDCN pathogenesis, but later reports did not confirm their correlation to the disease development (5-12). Clinically, the typical initial presentation of BPDCN is presence of asymptomatic cutaneous lesions that are subsequently followed by bone marrow involvement and leukemic dissemination (5, 10). The disease is characterized by highly aggressive clinical course. Although BPDCN respond to different types of chemotherapy, the responses are usually of short duration, and disease is most often fatal within a few years from diagnosis (5, 10).

Despite rare incidence of BPDCN, numerous variations from typical clinicopathological picture of BPDCN have been reported, such as different extracutaneous manifestation, lack of skin involvement, immunophenotypic variants or other, making a diagnosis even more complicated (13-17). In this paper we report two cases of BPDCN diagnosed in our center with objective to increase clinical awareness for these rare and aggressive malignancies that seem to be underdiagnosed in Poland.

63-year old man was referred to the Department of Chemotherapy of Medical University of Łódź in April 2008 for evaluation of potentially malignant skin lesions. The history of B symptoms was negative. On examination, the skin lesions were found to be predominantly purpuric nodules, in association with bruise-like areas, and were distributed over the left forearm. The majority of the nodules ranged from 1 to 2 cm in diameter. The nodules were not painful on palpation and the temperature of the adjacent skin was normal. On the physical examination lymphadenopathy, hepatomegaly or splenomagaly were excluded. The computed tomography scan of the chest and abdomen revealed no enlarged lymph nodes in the mediastinum or retroperitoneum. The complete blood count (CBC) was normal.

On the basis of histopathological and immunohistochemical examination of the full-layer skin biopsy the diagnosis of BPDCN was established (fig. 1A-D). The skin was shown to be involved by dense, diffuse infiltration of blastic cells with irregular nuclei and one to a few nucleoli (fig. 1D).

The epidermis was intact, while the infiltration was extended to subcutaneous fat (fig. 1 A, B, C). The variable number of mitoses was seen (fig. 1D). Immunohistochemical profile was determined as positive for LCA, CD4, CD43 and CD56, and negative for such lineage markers as CD3, CD8, CD20, CD30, myeloperoxidase (MPO) and terminal deoxynucleotidyltransferase (TdT) andgranzyme B. For differential diagnosis with other small blue round cell tumors staining with other markers were also performed, namely CD99 (-), CKMNF (-), CK20 (-), HMB45 (-), NSE-, TTF1 (-), CKAE1/AE3 (-), Melan A (-), Vimentin (+), and synaptophysin (-). Proliferative index of Ki -67 (MIB-1) reached 80%. Additionally, bone marrow aspiration was performed to exclude bone marrow involvement by BPDCN and shown normal marrow cytology. The treatment was based on standard chemotherapy protocol CHOP (cyclophosphamide, doxorubicine, vincristine and prednisone) protocol. The patient received seven CHOP cycles at 4-week intervals and achieved complete resolution of skin infiltrations.