Blastic plasmacytoid dendritic cell neoplasms: clinico-immunohistochemical correlations in a series of 91 patients.

Blastic plasmacytoid dendritic cell neoplasm is a rare clinicopathologic entity, characterized by strong skin tropism and a poor prognosis. The diagnosis is generally made by skin biopsy with appropriate immunohistochemical studies. To identify potential biological prognostic factors for blastic plasmacytoid dendritic cell neoplasm, we performed an extended clinico-immunohistochemical study on a series of 91 well-documented cases collected since 1995 by the French Study Group on Cutaneous Lymphomas. Skin biopsies were analyzed using a panel of 12 immunohistochemical markers (CD4, CD56, CD123, CD303, TCL1, CD68, CD2, CD7, TdT, Ki-67, S100, and MX-1). The results were correlated with survival. The 5 most characteristic markers of this entity (CD4, CD56, CD123, CD303, and TCL1) were expressed simultaneously in only 46% of patients. However, when 4 markers were expressed the diagnosis could still be reliably made without resorting to any additional stains. Expression of TdT and/or S100 correlated with varying degrees of maturation. Statistical survival analyses showed that CD303 expression and high proliferative index (Ki-67) were significantly associated with longer survival.