[Retrospective analysis of 4 cases of the so-called blastic NK-cell lymphoma, with reference to the 2008 WHO classification of tumours of haematopoietic and lymphoid tissues].

OBJECTIVE To study the clinical and pathologic features of 4 cases of the so-called blastic natural killer (NK)-cell lymphoma, with reference to the 2008 WHO classification of tumours of haematopoietic and lymphoid tissues. METHODS The clinical, pathologic and immunohistochemical findings (EliVision method) of 4 cases of blastic NK-cell lymphoma (previously diagnosed according to the 2001 WHO classification) were retrospectively analyzed and reclassified with a special reference to the 2008 WHO classification. RESULTS The 4 cases of hematologic malignancy studied were characterized by the presence of medium-sized blastic lymphoma cells, CD56 expression, and absence of lineage-specific B-cell, T-cell and myeloid cell markers. According to the 2001 WHO classification, they fell into the category of blastic NK-cell lymphoma. Three of the cases presented with primary cutaneous lesions and expression of CD56, CD4 and CD123. They are likely derived from the plasmacytoid dendritic cells rather than NK cells. They were then, according to the 2008 WHO classification, reclassified as the blastic plasmacytoid dendritic cell neoplasm. The remaining case showed lymph node involvement, positive for CD56 and CD4, negative for CD123, and not accompanied with the cutaneous lesions. This case was provisionally classified as a ambiguous lineage leukemia-NK cell lymphoblastic leukemia/lymphoma. CONCLUSIONS The so-called blastic NK-cell lymphomas in the 2001 WHO classification are rare and represent a heterogeneous group of lymphoproliferative disorders, with different clinical, pathologic and immunohistochemical features. It's suggested to have a precise category when applying the 2008 WHO classification to this kind of lesion.