Biological effects of recombinant human granulocyte colony-stimulating factor in patients with untreated acute myeloid leukemia

Hematopoietic growth factors are being administered to patients with acute myeloid leukemia (AML) both to shorten the duration of chemotherapy-induced neutropenia and in an attempt to increase cytotoxicity of cell cycle-specific agents. However, limited information is available concerning the effects of growth factors in AML patients. To examine the in vivo effects of recombinant human granulocyte colony-stimulating factor (G-CSF) on AML cells, laboratory studies were performed before and after a 72-hour intravenous infusion of G- CSF (10 μg/kg/d) administered to 28 untreated AML patients. Twenty-seven patients (96%) showed increases in at least one of the following parameters after G-CSF: blood blasts, bone marrow (BM) blasts, leukemia cells in S phase or interphase cells with leukemia-specific markers shown by fluorescence in situ hybridization. The median paired change in absolute blast count was +2.7 x 10⁹/L (P = .0001) after G-CSF, as compared with 0.0 during the 72 hours before initiation of G-CSF. The median percentage of BM leukemia cells in S phase increased from 6.0% to 10.7% after G-CSF (median change, +5.9%; P = .009). Interphase BM cells with trisomy 8 or monosomy 7 increased in 6 of 6 patients with these abnormalities (P = .02), with a median percent increase of 47%. Blood neutrophil counts also increased during G-CSF (median paired change, +2.8 x 10⁹/L; P < .0001). Trisomy 8 or monosomy 7 was shown by fluorescence in situ hybridization in post-G-CSF blood neutrophils from 4 of 6 patients but was also present in neutrophils before G-CSF. We conclude that the percentage of leukemia cells in S phase increases and that leukemic cell populations undergo expansion during short-term administration of G-CSF in almost all AML patients.