John RP Tesser, Daniel E Furst, Ira Jacobs

Extrapolation is the approval of a biosimilar for use in an indication held by the originator biologic not directly studied in a comparative clinical trial with the biosimilar. Extrapolation is a scientific rationale that bridges all the data collected (ie, totality of the evidence) from one indication for the biosimilar product to all the indications originally approved for the originator. Regulatory approval and marketing authorization of biosimilars in inflammatory indications are made on a case-by-case and agency-by-agency basis after evaluating the totality of evidence from the entire development program. This totality of the evidence comprises extensive comparative analytical, functional, nonclinical, and clinical pharmacokinetic/pharmacodynamic, efficacy, safety, and immunogenicity studies used by regulators when evaluating whether a product can be considered a biosimilar. Extrapolation reduces or eliminates the need for duplicative clinical studies of the biosimilar but must be justified scientifically with appropriate data. Understanding the concept, application, and regulatory decisions based on the extrapolation of data is important since biosimilars have the potential to significantly impact patient care in inflammatory diseases.