MYELOID BIOLOGY: Edited by David C. Dale
Twenty years ago the colony-stimulating factors (CSFs) were approved for use in the prevention of neutropenia – granulocyte colony-stimulating factor (G-CSF) to prevent chemotherapy-induced neutropenia and granulocyte-macrophage colony-stimulating factor (GM-CSF) to accelerate marrow recovery after bone marrow transplantation. This development was preceded by three decades of work – from the discovery of the CSFs, through the cloning of the genes for the hematopoietic growth factors, and scaling up production to make clinical uses feasible . Two decades later it is easy to see their enormous impact on the care of our patients.
Twenty years ago, chemotherapy-induced neutropenia was the dose-limiting adverse effect of cancer chemotherapy, and it still is today. The difference is that the problem can now be better managed chiefly because of the potency of G-CSF to accelerate marrow recovery if given 1–3 days after the myelotoxic chemotherapy. After the initial pivotal trials, several years of research were needed to establish indications and guidelines for appropriate use, and these guidelines have needed regular updates to match changes in cancer treatment regimens [2–4]. A key concept now is that myeloid growth factor treatment should be determined based on patient-specific risk factors – the nature of the patient's underlying disease, the myelotoxicity of the planned chemotherapy and the health status and comorbidities of the patient . Recent evidence from meta-analyses indicates that G-CSF can both prevent febrile neutropenia during the period of chemotherapy and facilitate more intense chemotherapy for better cancer treatment outcomes [5,6].
The use of the CSFs for the treatment of chronic neutropenia has had a parallel history. In the late 1980s, several small trials suggested that they might be of use as long-term therapies for neutropenia. A randomized trial of G-CSF for treatment of cyclic, congenital and idiopathic neutropenia then established its effectiveness to correct neutropenia and prevent infections in this population . The Severe Chronic Neutropenia International Registry has prospectively followed the patients from the initial trials and additional patients to show the long-term effectiveness of this therapy . This registry also provided the clinical information for an increasingly precise description of the rare hematological diseases causing severe chronic neutropenia and the discovery of the specific causal genetic defects.
One of the challenging issues with use of the CSFs is whether they can cause myelodysplasia or leukemia. Twenty years has not answered this question, because it is so difficult to study. With cancer chemotherapy, we know that many of the standard agents used are both myelotoxic and leukemogenic. Because the CSFs permit more intensive therapy, it might be expected that combining CSFs with more myelotoxic treatments would be associated with greater risk. This indeed was the finding in a recent study, the same study that showed that, overall, more intensive chemotherapy with CSF support promoted long-term survival . In patients with severe chronic neutropenia, one patient group, those with severe congenital neutropenia, who are known to have an intrinsic risk of leukemia, had about a 20% risk of developing myelodysplasia (MDS) or acute myeloid leukemia (AML) with long-term G-CSF treatment . Other patient groups showed no apparent risk of MDS or AML with long-term G-CSF therapy. Current evidence suggests that the risk of AML associated with CSF administration must be small, but it is difficult to envision how a definitive study will ever be conducted.
To be sure, many questions remain about the CSFs: appropriate use, cost benefits, combinations, adverse effects, alternatives and bio-similars. Nevertheless, twenty years after their introduction the CSFs have become an integral part of the practice of hematology and oncology.
Conflicts of interest
D.C.D. is a consultant for Amgen, the manufacturer of G-CSF, and conducts research on neutropenia with the support of Amgen and the National Institutes of Health.
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