Abrogating chemotherapy-induced myelosuppression by recombinant granulocyte-macrophage colony-stimulating factor in patients with sarcoma: Protection at the progenitor cell level

Purpose: The purpose of this study was to optimize the dose, schedule, and timing of recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) administration that would best abrogate myelosuppression in patients with sarcoma. Patients and Methods: Sarcoma patients who had experienced severe myelosuppression after chemotherapy with Cytoxan (cyclophosphamide; Bristol-Myers Squibb Co, Evansville, IN), Adriamycin (doxorubicin; Adria Laboratories, Columbus, OH), and dacarbazine ([CyADIC], cycle 1) were eligible. GM-CSF was administered during a 14-day period until 1 week before cycle 2 of CyADIC and was resumed 2 days after cycle 2 completion. The schedule subsequently was modified to allow the earlier administration of GM-CSF in which CyADIC was compressed from 5 days to 3 days, and GM-CSF was administered immediately after the discontinuation of CyADIC in cycle 2. To understand better the impact of GM-CSF on bone marrow stem cells, the proliferative status of bone marrow progenitors was examined during treatment. To evaluate the effects of GM-CSF on effector cells, select functions of mature myeloid cells were also examined. Results: In the seven patients who were treated on the initial schedule, GM-CSF enhanced the rate of neutrophil recovery; however, severe neutropenia was not abrogated. By using the modified schedule in 17 patients, GM-CSF significantly reduced both the degree and the duration of neutropenia and myeloid (neutrophils, eosinophils, and monocytes) leukopenia. The mean neutrophil and mature myeloid nadir counts were 100/mm³ and 280/mm³ in cycle 1 and 290/mm³ and 1,540/mm³ in cycle 2 (P < .01 and P < .001). The duration of severe neutropenia (neutrophil count < 500/mm³) and myeloid leukopenia (myeloid leukocyte count 1,000/mm³) were reduced from 6.2 and 6.8 days in cycle 1 to 2.8 and 1.4 days in cycle 2 (P < .001). While 16 of 17 patients experienced severe myeloid leukopenia (< 500/mm³) in cycle 1, only two of 17 experienced severe myeloid leukopenia in cycle 2 (P < .001). Overall, severe neutropenia was abrogated in seven patients, which made them eligible for dose-escalation of Adriamycin. The fraction of cycling progenitors increased threefold on GM-CSF and decreased dramatically below the baseline within 1 day of GM-CSF discontinuation. Conclusions: The modified schedule improved the beneficial effects of GM-CSF by enhancing myeloprotection and permitting dose-intensification of chemotherapy. The increased myeloid mass and quiescent progenitors at the initiation of chemotherapy suggest that GM-CSF might allow further chemotherapy dose-rate intensification by shortening the interval between courses.