Clinical equivalence with G-CSF biosimilars: methodologic approach in a (neo)adjuvant setting in non-metastatic breast cancer

Biosimilars are biological medicines that have been shown to be similar to a reference biological medicine that has already been approved for use. Development of biosimilars is based on a “totality of evidence” approach that involves a series of steps by which biosimilars must demonstrate similarity to a reference product in all aspects of the drug and eliminate any remaining uncertainties. Clinical studies are then considered confirmatory and are performed to show that there are no clinically meaningful differences compared with the reference product in a sensitive patient population. The recombinant human granulocyte colony-stimulating factor (G-CSF) biosimilar EP2006/Zarxio® (filgrastim-sdnz) became the first FDA-approved biosimilar in 2015. This review evaluates how clinical equivalence can be demonstrated with G-CSF biosimilars through the identification of “sensitive” study populations and endpoints. Patients with non-metastatic breast cancer treated in the (neo)adjuvant setting represent a potentially homogenous population, making this a suitable sensitive indication for assessing filgrastim and pegfilgrastim biosimilars compared with reference products. This review includes clinical trials of G-CSF biosimilars in breast cancer, focusing on key aspects of the trials that were necessary to accurately demonstrate clinical equivalence and enable extrapolation to relevant indications, based on guidelines and biostatistical principles.