Bone marrow macrophages in Waldenström's macroglobulinemia: a report of four cases.

It is well known that some B-cell lymphomas are accompanied by a prominent epithelioid cell response, caused by activated macrophages, such as marginal zone B-cell lymphoma of a mucosa-associated lymphoid tissue. We investigated six bone marrow samples from four cases of Waldenström's macroglobulinemia and report a unique observation that large conjugates of tumor cells around a macrophage were prominent in all cases, particularly in one case, the bone marrow of which contained increased CD163-positive macrophages. Mast cells were increased in all the samples, some of which seemed to be in close contact with tumor cells. We consider that the conjugates represented close interactions of tumor cells, macrophages, and mast cells by cell-to-cell contact. Three of the present cases showed a favorable course. On the other hand, one case suffered from severe anemia and thrombocytopenia due to hemophagocytic syndrome at the second admission and showed a severe clinical course. Clinicians should be aware of the risk of lymphoma-associated hemophagocytic syndrome in this low-grade lymphoma, although many of the patients with hemophagocytic syndrome in Japan have aggressive lymphomas such as diffuse large B-cell lymphoma.