Future directions with hematopoietic growth factors

Myelosuppression is a common dose-limiting factor for many cancer patients receiving cytotoxic treatment. It also contributes to the need for hospitalization, intravenous antibiotic administration, transfusion of blood products, and treatment delays. In the past decade, several hematopoietic growth factors have become available for attenuating hematologic toxicity of chemotherapy. Although the use of myeloid growth factors and erythropoietin has reduced the severity of neutropenia and anemia, these growth factors require frequent injections and, in some cases, frequent visits to healthcare facilities. Recently, the longer acting hematopoietic growth factors pegfilgrastim (Neulasta) and darbepoetin alfa (Aranesp) have been developed. Pegfilgrastim has shown safety and efficacy similar to those of standard granulocyte colony-stimulating factor (filgrastim) and provides the convenience of once-per-cycle dosing. Darbepoetin alfa, because of its long half-life, provides scheduling flexibility and can be administered at 1-, 2-, or 3-week intervals. The recent data from trials with recombinant human thrombopoietin also suggest that multiple daily dosing may not be required with this agent. The prognostic value of anemia and the impact of erythropoietin on tumor response and survival are under active investigation. Future directions will probably involve the use of new agents designed with the needs for infrequent dosing, less potential for immunogenicity and toxicity, and an expanding role in improving overall treatment outcome in mind.