The objectives of this study were to simulate for the European Union G5 countries the potential cost savings of converting patients from originator granulocyte colony-stimulating factor (G-CSF) filgrastim and pegfilgrastim to a biosimilar filgrastim, to evaluate how reallocating these savings could increase patient access to antineoplastic therapy, and to estimate the number of patients needed to convert to provide antineoplastic treatment to one patient.