The first anticancer biosimilars have entered clinical use, with many others under clinical development. Like all biologics, biosimilars may elicit unwanted immune responses that can significantly impact clinical efficacy and safety. Head-to-head immunogenicity assessment of biosimilars and their reference biologics should, therefore, be a critical component of a biosimilar's clinical development program. Various bioanalytical platforms may be used to detect and characterize immune responses, each having relative strengths and weaknesses. To fully recognize the clinical relevance of such data, regulators must be able to interpret immunogenicity results in an assay-specific context as well as in perspective of clinical pharmacology, efficacy and safety. Herein, we discuss current challenges imposed by global regulatory requirements for immunogenicity assessment of biosimilars.

From the scarce data available, the consequences of switching between reference product mAbs and their biosimilar(s) in the oncology setting are as yet unknown. Additional clinical evidence from well-designed switching studies is needed to guide switching decisions.

Introduction: Biologics are highly complex drugs and many of their characteristics are defined by the manufacturing process. In recent years, several monoclonal antibody (mAb) biologics, which were hitherto only available for intravenous (IV) administration, have been reformulated for subcutaneous (SC) administration. Reformulation involves alterations to the established manufacturing process and it has been argued that a SC formulation should therefore be considered a biosimilar version of its previously approved IV formulation. Areas covered: Developing an SC version of an approved IV mAb product requires the adaptation of its formulation and route of administration. This process is illustrated via case examples of trastuzumab and rituximab and summarize what data requirements support the regulatory approval of these new formulations. Furthermore, we discuss similarities and differences between the development of an SC product vs. the development of a biosimilar. Expert opinion: The production process of a biosimilar is independently established from the very beginning, while the development of an SC formulation affects later stages of an already established production process and builds on extensive experience with the IV formulation. Considering these fundamentally different situations, a biologic product reformulated for SC administration should not be considered a 'biosimilar' version of itself. ARTICLE HISTORY