Hematopoietic growth factors in acute myeloid leukemia: supportive and priming effects.

Hematopoietic growth factors (GFs) are administered to patients who have acute myeloid leukemia (AML) in order to overcome two limitations of chemotherapy: (I) myelotoxicity, and (2) the chemoresistance of minimal residual disease. GFs have been used after chemotherapy in 11 clinical studies, 8 on older age or otherwise high-risk AML. The GFs used were granulocyte-macrophage colony-stimulating factor (GM-CSF) in 7, G-CSF in three and macrophage-CSF in one of the studies. Beneficial effects could be shown on the duration of neutropenia in 8 studies, frequency of infections or fever in 4 studies, mortality or survival in 2 studies and remission rate in 1 study. The benefits in remissions and survival were all found among high-risk patients. One study in younger patients found disadvantages in the remission rate and event-free survival, whereas there was no adverse effect of GF on therapy resistance, leukemic regrowth, or disease-free survival in the other studies. GF priming strategies are based on their stimulation of AML blasts in vitro, their modulation of cellular cytarabine (ARA-C) metabolism and enhancement of clonogenic cell kill by ARA-C. Protective effects of GF against clonogenic cell kill or apoptosis were also described. There are data from 10 clinical studies using GFs before or simultaneously with chemotherapy. One study showed significance, two others a tendency to longer disease-free survival, and two studies showed a trend toward more remissions. A disadvantage in the remission rate and survival was found in one study and prolonged thrombocytopenia in two studies. Nine of ten studies did not find evidence for an adverse effect of GF priming on the course of the disease. In most studies, GF priming was only administered in one or two chemotherapy courses. One study giving four to five courses found a reduction in relapses during the first 6 months. In conclusion, a supportive use of GF may have a place in high-risk, but not standard-risk AML. GF priming approaches may not have been adequately investigated and an extension of this strategy to more treatment courses now appears more promising. Based on the clinical data available, all administration of GF in AML should be regarded as investigational.