EVIDENCE FOR A LYMPHOTROPIC NATURE OF CIRCULATING PLASMACYTOID MONOCYTES - FINDINGS FROM A CASE OF CD56(+) CHRONIC MYELOMONOCYTIC LEUKEMIA

Because the cells previously designated plasmacytoid T cells share maj or immunophenotypic features with cells of the mononuclear-phagocyte s ystem, they have been re-named and are now known as plasmacytoid monoc ytes (PM). We describe a unique case of chronic myelomonocytic leukemi a with circulating PM. The patient, a 48-year-old man, presented initi ally with refractory anemia. Four years later his general condition de teriorated, accompanied by an increase in leukocytes to 200000/mu l bl ood. The bone marrow histology was interpreted as compatible with a di agnosis of chronic myelomonocytic leukemia. Two months before he died, the patient developed generalized lymphadenopathy clinically simulati ng malignant lymphoma. Histologic examination of an axillary lymph nod e revealed diffuse infiltration by PM. The PM in the lymph node and so me circulating cells closely resembling PM expressed L-selectin, a fin ding that could be interpreted as a morphologic correlate of their mar ked lymphotropism. The detection of large numbers of CD56/CD33 double- positive circulating blast cells by FAGS analysis strongly supported t he diagnosis of a leukemia of myelogenous origin. The patient died of tumor cachexia. Autopsy revealed widespread leukemic infiltrates (alwa ys containing clusters of PM) in bone marrow, spleen, liver, lymph nod es, and mucosa-associated lymphoid tissue of the oropharynx. The final diagnosis was one of chronic myelomonocytic leukemia with marked lymp hotropism and partial differentiation towards PM. We consider that the rare instances of a hematologic tumor with differentiation towards PM should be classified amongst the myelogenous leukemias.