Granulocyte Colony-Stimulating Factor: Key (F)actor or Innocent Bystander in the Development of Secondary Myeloid Malignancy?

Granulocyte colony-stimulating factor (G-CSF), the major cytokine involved in the control of neutrophil production, is used in the clinic for treatment of congenital and acquired neutropenias and to reduce febrile neutropenia before or during courses of intensive cytoreductive therapy. In addition, healthy stem cell donors are treated with G-CSF for mobilization of hematopoietic stem cells in the peripheral blood. Recent studies have uncovered novel roles for G-CSF in myocardial regeneration following cardiac infarction ( 1 – 3 ) and in ameliorating programmed cell death in neuronal cells caused by acute ischemic stroke, thereby reducing the volume of the brain infarct ( 4 ). Thus, it may be anticipated that the therapeutic application of G-CSF will increase considerably in the near future, making careful and timely risk assessment of vital importance. In this issue of the Journal, Hershman et al. ( 5 ) report a two fold increased risk of secondary myelodysplasia (MDS) or acute myeloid leukemia (AML) in breast cancer patients who received G-CSF (or granulocyte-macrophage CSF) during adjuvant chemotherapy, compared with patients who did not receive growth factor treatment. This and other recent studies raise questions concerning the underlying molecular and cellular mechanisms whereby myeloid growth factors would initiate or accelerate the development of MDS/AML and how to deal with the potential