Leukemia-associated lymph node infiltrates of plasmacytoid monocytes (so-called plasmacytoid T-cells). Evidence for two distinct histological and immunophenotypical patterns.

The medium-sized mononuclear cell with plasmacytoid features, formerly known as "T-associated plasma cell" or "plasmacytoid T cell," has recently been shown to express several myelomonocyte and monocyte-macrophage associated antigens, suggesting a monocytic origin, and it has been renamed "plasmacytoid monocyte." The present study describes the clinical and pathological features of two patients with generalized lymphadenopathy and leukemia (chronic myelomonocytic leukemia in Case 1, and acute non-B, non-T lymphoblastic leukemia in Case 2), and whose lymph node biopsies showed large numbers of plasmacytoid monocytes associated with the leukemic infiltrates. Case 1 was strikingly similar to three previously reported cases of so-called "plasmacytoid T cell" lymphoma, all associated with a myeloproliferative disorder. In our case, the destructive growth pattern of the plasmacytoid monocytes and the de novo expression of CD5 on these cells favored their neoplastic nature; the sharing of some markers of plasmacytoid monocytes with the myelomonocytic infiltrate suggested they were part of the tumoral proliferation. In Case 2, plasmacytoid monocytes displayed an immunophenotype guide similar to that reported in reactive conditions and were antigenically unrelated to the leukemic cells; plasmacytoid monocyte clusters occurred also in the lymphoid parenchyma spared by the leukemic infiltrate. These findings led us to interpret the large numbers of plasmacytoid monocytes in this second case as a tumor-associated host reaction.