A pilot study of the biologic and therapeutic effects of granulocyte colonystimulating factor (filgrastim) in patients with acute myelogenous leukemia

In a carefully monitored pilot study, the in vivo biologic effects of filgrastim were investigated in eight patients with relapsed/refractory acute myelogenous leukemia. Within each patient, filgrastim was administered as a single agent prior to any chemotherapy in escalating doses of 0.12-6.0 μg/kg/day as a continuous intravenous infusion. The dose was increased every 14 days until an ANC of ≥2500/mm³ had been achieved or there was evidence of proliferation of the leukemia. In patients who demonstrated growth of the leukemic clone, cytosine arabinoside was initiated at 200 mg/m²/day for 5 days. Throughout the course of therapy, the effects of filgrastim on maturation and proliferation were assessed by in vitro studies of bone marrow aspirates. Three patients demonstrated a sustained increase in ANC; one achieved a partial remission and remained on therapy for 31 weeks. Two of the three responding patients had hypocellular marrows at the time of initiating filgrastim and demonstrated a low but normal pattern of growth in CFU-GM assay early in the treatment course. This suggested that these two characteristics may define an environment in which filgrastim can induce a growth advantage for the normal residual hematopoietic elements. In this study of selected patients, filgrastim appeared safe.