Recombinant human granulocyte-macrophage colony-stimulating factor reduces hematologic toxicity and widens clinical applicability of high-dose cyclophosphamide treatment in breast cancer and non-Hodgkin's lymphoma.

High-dose administration of anticancer agents is attractive both on theoretic and clinical grounds. Yet, high-dose regimens are usually used as salvage treatments, mainly as a consequence of their considerable hematologic toxicity. One pertinent example is represented by cyclophosphamide, an alkylating agent with a wide spectrum of marked antitumor activity. When used at doses up to 7 g/m2 (190 to 200 mg/kg) this drug does not cause myeloablation, but induces a severe, albeit transient, myelosuppression, which requires platelet transfusions in approximately 50% of treated patients, and is frequently complicated by infectious episodes, occasionally lethal. To accelerate hematopoietic recovery, we continuously infused for 14 consecutive days 5.5 micrograms/kg/d of the glycosylated human recombinant granulocyte-macrophage colony-stimulating factor (rhGM-CSF) into 15 patients with breast cancer and non-Hodgkin's lymphoma treated with 7 g/m2 cyclophosphamide. This schedule was chosen having obtained the fastest hematopoietic recovery among four different options during an initial schedule-finding phase on 12 overall patients. Twenty-one comparable subjects with solid tumors served as controls. We report here that this relatively low, well-tolerated dose of rhGM-CSF reduces from 20 to 14 (median) and from 24 to 14, the number of days required to recover circulating granulocyte counts over 1,000 and 2,500/microL, respectively. The stimulatory effect was associated with a remarkable clinical benefit. In fact, treated patients experienced less infectious complications (7% v 24%) were eligible to receive chemotherapy earlier (median, by day +14 v day +20 for controls), and fewer required prophylactic platelet transfusions (13% v 43%). Our results show that even very high doses of cyclophosphamide can be administered with improved hematologic toxicity, tolerable morbidity, and reduced supportive care requirements. The increase in the therapeutic index made possible by rhGM-CSF infusion prompts the use of high-dose cyclophosphamide, and possibly of other agents with similar myelotoxic activity, early in the clinical course of chemotherapy-sensitive tumors.