Bone marrow histiocytic proliferation in association with colony-stimulating factor therapy

A 6-year-old white male had a myelodysplastic syndrome (refractory anemia with excess blasts in transformation) and was treated with high dose chemotherapy. A combined esterase stain of the marrow blasts showed granulocytic differentiation. Subsequently, persistent pancytopenia with a severely hypocellular bone marrow developed, which was treated with a combination of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor. Sixteen days after the initiation of therapy, histologic examination of the bone marrow revealed a marked proliferation of histiocytes. To the best of the authors' knowledge, this is the first report of histiocytic proliferation in the bone marrow after colony-stimulating factor therapy.