CD4+/CD56+ hematodermic neoplasm: presentation of 2 cases and review of the concept of an uncommon tumor originated in plasmacytoid dendritic cells expressing CD123 (IL-3 receptor alpha).

CD4/CD56 hematodermic neoplasm is a rare neoplasm presenting with cutaneous nodules, lymphadenopathy, bone marrow infiltration, and an aggressive clinical course. Recently, the plasmacytoid dendritic cell origin of this neoplasm has been demonstrated. Plasmacytoid dendritic cell is a hematopoietic-derived cell implicated in the regulation of innate and adaptive cell immunity and in the production of certain regulatory cytokines. Recently it has been demonstrated that these cells express cell surface markers such as IL-3 receptor alpha (CD123). In the present report, we describe the clinical, histologic, and immunohistochemical characteristics of 2 cases of CD4/CD56 hematodermic neoplasm. Both patients were male and the age at the time of diagnosis was 36 and 75 years, respectively. Clinical findings were limited to the skin and consisted of multiple cutaneous nodules located in the thorax and extremities, some of them ulcerated. Histologically, the tumors were characterized by a nonepidermotropic, dermal and subdermal infiltration of homogeneous medium-sized cells resembling lymphoblasts or myeloblasts. Immunohistochemical characterization of the tumors showed expression of CD4, CD56, CD43, and CD123, whereas CD8, CD20, and MPO were negative. Immunoreactivity for CD3, which has been described in rare occasions, was found only in one of the cases. This characteristic profile in addition to the expression of CD123, which was detected in both cases, can be used as valuable tools in the diagnosis of this rare neoplasm.