INTRODUCTION
The application of biologics to treat moderate-to-severe psoriasis has proven safe and ef cacious but their cost has been prohibitive for more widespread use.1 As patents on these (‘reference’, ‘originator’) biologic therapies end, the production and use of biosimilars (‘follow-on biologics’) will inevitably become more common. Per the Biologics Price Competition and Innovation (BPCI) Act, an abbreviated licensure pathway under the United States (U.S.) Affordable Care Act (ACA), a biosimilar “is a biological product that is highly similar to the reference product notwithstanding minor differences in clinically inactive components and that there are no clinically meaningful differences between the biological product and the reference product in terms of the safety, purity, and potency of the product.”2 Guidelines for developing biosimilar drugs are available from the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA).3,4,5 Conceptually, biosimilars are anticipated to introduce significant bene ts to the healthcare industry.Their increased cost savings potential could grant accessibility and adherence to a large population of patients who previously could not afford biologics, including those in developing countries.1 For the U.S. Medicare program alone, the application of biosimilars in healthcare is expected to result in a cost savings of $9 billion to $12 billion over the next decade.1,6Biosimilars, while likened to generic pharmaceuticals, are unlike small molecule pharmaceuticals. The International Psoriasis Council has released guidelines for standardizing pre-clinical assessments of emerging biosimilars via the development of a biosimilar index.7 Biologic pharmaceuticals are large complex organic biopolymers that cannot be replicated entirely identical to their reference biologics due to the nature of variability in the living systems and manufacturing techniques they are produced in.8 These inherent characteristic differences in biosimilars are the source of concern for potential safety and efficacy issues involving their pharmaceutical quality and properties of indication extrapolation, interchangeability, and immunogenicity (Table 1). Extrapolation of clinical data allows a biosimilar to be approved for therapeutic indications for which it has not been clinically
