What Is Filgrastim? Definition and What Research Reports

Filgrastim is a recombinant form of human granulocyte colony-stimulating factor (G-CSF), a haematopoietic growth factor. In the published literature the name refers to a non-glycosylated, Escherichia coli–expressed version of the human G-CSF protein carrying an additional N-terminal methionine residue, which is why it is sometimes written as "r-metHuG-CSF". It is a full-length recombinant protein of roughly 175 amino acids rather than a short synthetic peptide, and it is the reference molecule against which pegylated, tbo- and biosimilar variants are compared in clinical studies.

This page is for educational purposes only and is not medical advice; consult a licensed physician for any question about a medical condition or treatment. Nothing here describes how filgrastim is used in practice — it summarises what published papers reported.

Molecular Class and Origin

Filgrastim belongs to the colony-stimulating factor family of cytokines. Endogenous G-CSF is produced by monocytes, fibroblasts and endothelial cells; filgrastim is the recombinant analogue of that native protein, manufactured by bacterial expression rather than isolated from human tissue. Because the bacterial host does not glycosylate proteins, filgrastim differs from native human G-CSF in carbohydrate content while retaining the same amino acid backbone plus the extra methionine.

Several structurally related molecules share the stem name and appear alongside filgrastim in trial reports:

How the Term Is Used in Peptide and Protein Research

Within the broader "research peptide" vocabulary, filgrastim is frequently grouped with peptide and protein therapeutics because it is a sequence-defined, recombinantly expressed biologic. Strictly speaking it sits in the biologic protein category rather than the synthetic peptide category: it is too large to be made by routine solid-phase peptide synthesis and is instead produced by fermentation and purification. Readers encountering the word in a peptide glossary will most often see it used in three ways:

• As a named molecule — the specific recombinant G-CSF product described above.
• As a comparator — the benchmark against which pegylated, tbo- and biosimilar G-CSF products are measured, as in a 2018 multiple myeloma mobilisation comparison (PMID 29398647).
• As a mechanistic probe — a tool for studying G-CSF receptor signalling and progenitor cell biology, for example in work examining filgrastim in relation to fibrinolysis and neovascularization (PMID 35175691).

What the Published Literature Reports

Stem cell mobilisation and transplantation

The largest body of filgrastim literature concerns haematopoietic stem cell mobilisation and engraftment. Researchers compared pegylated filgrastim with filgrastim for stem cell mobilisation in multiple myeloma patients after novel agent induction in a 2018 report in Clinical Lymphoma, Myeloma & Leukemia (PMID 29398647). A separate retrospective review examined tbo-filgrastim versus filgrastim for mobilisation and engraftment in autologous haematopoietic stem cell transplant patients (PMID 30854925). Innovator filgrastim was compared with a generic version for mobilisation in a South Asian transplantation series (PMID 34938680), and the efficacy and safety of a biosimilar filgrastim in the cord blood transplantation setting was the subject of a single-institution retrospective analysis (PMID 30577272).

Supportive care in chemotherapy and cell therapy

Filgrastim and pegfilgrastim were compared for outcomes of dose-adjusted R-EPOCH chemotherapy in non-Hodgkin's lymphoma in a 2021 Supportive Care in Cancer paper (PMID 33594515). The molecule has also been examined in the context of chimeric antigen receptor (CAR) T-cell therapy, where a 2021 study in the International Journal of Cancer reported on filgrastim associations with CAR T-cell therapy (PMID 33091961).

Non-oncology and preclinical settings

Outside haematology-oncology, filgrastim therapy was evaluated in kidney transplant recipients in a 2017 Progress in Transplantation report (PMID 29187137). In animal work, researchers studied the effect of filgrastim on adult male rats' fertility and reproductive performance in a 2021 paper in the Saudi Journal of Biological Sciences (PMID 33911967). Tissue-engineering research has looked at filgrastim in relation to fibrinolysis and neovascularization (PMID 35175691). These are laboratory and clinical research contexts, not descriptions of routine practice.

Filgrastim Adverse Events: What Studies Report

Published safety reports on filgrastim range from single case descriptions to institutional case series. Points the literature has documented include:

• Thrombocytopenia. A 2020 case report in BMJ Case Reports described filgrastim-induced thrombocytopenia in a single patient (PMID 32606115).
• Acute aortitis. Researchers reported on the incidence and clinical features of PEGylated filgrastim-induced acute aortitis in patients with breast cancer in a 2020 Scientific Reports paper (PMID 33122662).
• Tumour biology signals. A 2023 Medical Oncology paper examined breast tumour metastasis following filgrastim administration in relation to the SDF-1/CXCR4 pathway (PMID 36609711).
• Reproductive endpoints in animals. The study in adult male rats assessed fertility and reproductive performance outcomes after filgrastim exposure (PMID 33911967).

Case reports describe what happened to individual patients and cannot establish how frequently an event occurs; retrospective series describe associations observed in records rather than randomised comparisons.

Regulatory Status

Filgrastim is a licensed biologic medicine in the United States, the European Union and many other jurisdictions, and multiple biosimilar and follow-on versions have been authorised — which is why the comparative literature summarised above exists at all (PMID 34938680). Material sold under research-use-only (RUO) labelling is not a licensed medicine and is not intended for human administration. Regulatory categories vary by country and change over time.

Limitations of This Entry

This glossary stub defines a term and points to representative published work. It does not list doses, schedules, indications or comparative effectiveness conclusions, and the studies cited differ widely in design, population and endpoint — a retrospective single-institution analysis (PMID 30577272) and a rodent reproductive study (PMID 33911967) answer very different questions and are not interchangeable evidence. Anyone reading primary sources should check the full text rather than relying on a summary.

References

• Filgrastim induced thrombocytopenia (BMJ Case Reports, 2020)
• Filgrastim, fibrinolysis, and neovascularization (Journal of Tissue Engineering and Regenerative Medicine, 2022)
• Effect of Filgrastim on adult male rats' fertility and reproductive performance (Saudi Journal of Biological Sciences, 2021)
• Breast tumor metastasis following filgrastim administration due to the SDF-1/CXCR4 pathway (Medical Oncology, 2023)
• Pegylated Filgrastim Versus Filgrastim for Stem Cell Mobilization in Multiple Myeloma After Novel Agent Induction (Clinical Lymphoma, Myeloma & Leukemia, 2018)
• Filgrastim associations with CAR T-cell therapy (International Journal of Cancer, 2021)
• The incidence and clinical features of PEGylated filgrastim-induced acute aortitis in patients with breast cancer (Scientific Reports, 2020)
• Innovator Filgrastim versus Generic Filgrastim in Hematopoietic Stem Cell Transplantation Mobilization (South Asian Journal of Cancer, 2021)
• Tbo-filgrastim versus filgrastim for stem cell mobilization and engraftment in autologous hematopoietic stem cell transplant patients: A retrospective review (Journal of Oncology Pharmacy Practice, 2020)
• Efficacy and Safety of Biosimilar Filgrastim for Cord Blood Transplantation: A Single-Institution Retrospective Analysis (Transplantation Proceedings, 2018)
• Evaluation of Filgrastim Therapy in Kidney Transplant Recipients (Progress in Transplantation, 2017)
• Effects of filgrastim versus pegfilgrastim on outcomes of DA-R-EPOCH for non-Hodgkin's lymphoma (Supportive Care in Cancer, 2021)