Analytical Similarity Assessment in Biosimilar Studies.

For assessment of biosimilarity, the US Food and Drug Administration (FDA) recommends a stepwise approach for obtaining the totality-of-the-evidence for demonstrating biosimilarity between a proposed biosimilar product and an innovative (reference) biological product. The stepwise approach starts with analytical studies for functional and structural characterization at various stages of manufacturing process of the proposed biosimilar product. Analytical similarity assessment involves identification of critical quality attributes (CQAs) that are relevant to clinical outcomes. FDA proposes first classifying the identified CQAs into three tiers according to their criticality or risking ranking relevant to clinical outcomes and then performing equivalence test (for CQAs in Tier 1), quality range approach (for CQAs in Tier 2), and raw data or graphical presentation (for CQAs in Tier 3) for obtaining totality-of-the-evidence for demonstrating biosimilarity between the proposed biosimilar product with the reference product. In practice, some debatable issues are evitably raised due to this complicated process of analytical similarity assessment. In this article, these debatable are described and discussed.