Filgrastim is approved for treatment of neutropenia (low white blood cell count in the blood) and for the mobilization of peripheral blood stem cells in patients and healthy donors. Several filgrastim biosimilars have been licensed in Europe and, in all cases; all indications of the originator product were approved.

There has been criticism by some societies of the extrapolation to stem cell mobilization in healthy donors. However, the scientific arguments below support the extrapolation granted by EMA’s Committee for Medicinal products for Human Use:

• All licensed filgrastim biosimilars demonstrated a high level of similarity in molecular structure and biological activity with their reference products.
• Pharmacokinetic profiles were comparable ensuring equivalent exposure.
• All pharmacological actions of filgrastim are mediated via a single affinity class cell receptor. Therefore, comparable receptor binding is expected to result in comparable effects.
• Comparable pharmacodynamic activities were confirmed in healthy subjects and/or patients.
• The safety and immunogenicity profiles were found to be comparable to those of the reference product, in patients and in pharmacology studies in healthy subjects.

The fact that post-marketing studies have confirmed the efficacy and safety of filgrastim biosimilars in the approved indications including the mobilization of stem cells in healthy donors justifies EMA’s decision on extrapolation [2, 3].

*Extrapolation involves extending and applying the data from clinical studies regarding one medical condition to another medical condition.

Disclaimer
The authors of the research paper [1] declared that they are members or experts of the European Medicines Agency's (EMA) Biosimilar Medicinal Products Working Party (BMWP). This paper [1] represents solely the views of the authors and should not be understood or quoted as being made on behalf of or reflecting the position of EMA or its committees.

Conflict of interest
The authors of the research paper [1] declared that there were no conflicts of interest.

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References
1.   Weise M, Kurki P, Wolff-Holz E, Bielsky MC, Schneider CK. Biosimilars: the science of extrapolation. Blood. 2014 Oct 8. pii: blood-2014-06-583617. [Epub ahead of print]
2.   GaBI Online - Generics and Biosimilars Initiative. Mobilization of stem cells in healthy donors by G-CSF biosimilars shows comparable efficacy and safety to Neupogen [www.gabionline.net]. Mol, Belgium: Pro Pharma Communications International; [cited 2014 Nov 21]. Available from: www.gabionline.net/Biosimilars/Research/Mobilization-of-stem-cells-in-healthy-donors-by-G-CSF-biosimilars-shows-comparable-efficacy-and-safety-to-Neupogen
3.   GaBI Online - Generics and Biosimilars Initiative. Biosimilar G-CSF safe for mobilization of stem cells [www.gabionline.net]. Mol, Belgium: Pro Pharma Communications International; [cited 2014 Nov 21]. Available from: www.gabionline.net/Biosimilars/Research/Biosimilar-G-CSF-safe-for-mobilization-of-stem-cells 

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