Therapy with myeloid colony-stimulating factors has been safely and effectively used in a wide variety of situations associated with neutropenia. We present a case of pseudoleukemia occurring in a patient with lymphoma and pancytopenia after 2 days of treatment with granulocyte colony-stimulating factor (G-CSF). Bone marrow aspirate and flow cytometry study results were consistent with acute myelomonocytic leukemia but were normal after G-CSF was discontinued for 4 days. As previous phase I studies of bone marrow morphology after G-CSF use have not described the extreme myeloid immaturity seen in this patient, it seems likely that the action of G-CSF was enhanced by factors associated with the patient’s illness. We emphasize the clinical importance of this case in light of the widespread use of G-CSF.
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