Q: What is extrapolation and what role does extrapolation play in biosimilar approval?
A: Extrapolation allows a biosimilar candidate to potentially be approved for use in indications approved for the reference product, even if those indications were not studied as part of the clinical development program for a biosimilar.
An example of extrapolation of data is the introduction of a new subcutaneous formulation of an IV applied product. Although the formulation and bioavailability of the subcutaneous product will be different, one clinical study is usually sufficient to grant several, if not all, clinical indications approved for the IV product.
However, extrapolation is not automatic. Scientific justification for extrapolation of claims of safety and efficacy for the tested and extrapolated indications must address whether the mechanism of action is expected to differ across indications; whether the product’s PK/PD and biodistribution is expected to vary across patient populations; whether the product’s immunogenicity is expected to vary in different patient populations; and whether there are differences in toxicity in different indications and patient populations.