Biosimilars 101: considerations for U.S. oncologists in clinical practice.

Biosimilars of biologics used for cancer treatment and supportive care are expected to enter the U.S. market soon. Biosimilars will be highly similar to their reference products, but unlike generic drugs, not identical. Differences between a biosimilar and its reference product may arise because of the complexity of biologics, and differences in the cell lines and processes used during manufacturing. Biosimilars will be approved in the United States through a regulatory pathway based on comparative analytical and clinical studies for their characterization and demonstration of no clinically meaningful differences from their reference products. Unlike generics, initial approval may not include interchangeability, as additional evidence may be required before a biosimilar could be approved as interchangeable with its reference product; interchangeable designation could allow pharmacy-level substitution without prescriber intervention. In some cases, the U.S. Food and Drug Administration (FDA) may extrapolate an indication that has not been formally investigated for the biosimilar but that is approved for the reference product. Robust safety monitoring of all biologics is important to track and accurately attribute adverse events, particularly because their inherent complexity and manufacturing differences make them susceptible to structural changes that can affect safety (e.g., immunogenicity). Accuracy of postapproval safety reports will partly depend on the biosimilar naming approach. Potential cost savings should be evaluated in the context of differences in manufacturers' patient-assistance programs, copayments, and institutional costs. A manufacturer's ability to ensure reliable supply of high-quality biosimilars should also be considered. Broad understanding of these issues is critical for oncologists preparing for their use in clinical practice.