Trastuzumab Biosimilars: Evaluating their Potential for Fda Interchangeability

Abstract

Herceptin (trastuzumab) has been the backbone of HER2-positive breast and gastric cancer treatment since 1998. Several biosimilar versions now have regular FDA approval. But none are designated "interchangeable" by the Food and Drug Administration, a classification that allows a pharmacist to substitute a biosimilar without consulting the prescriber first. This review fills this gap: does the evidence already collected on trastuzumab biosimilars meet the interchangeability bar set by the 2009 Biologics Price Competition and Innovation Act? The scope is intentionally limited. Rather than re-litigating the clinical outcomes in detail, the paper reviews existing analytical, pharmacokinetic, clinical and post-marketing data against each of the regulatory requirements in turn, relying on FDA guidance, statutory language, agency records and literature published through March 2026. But one development changes the calculus significantly: The FDA draft guidance in June 2024 abandoned the long-standing expectation of a dedicated switching study. Two approvals since then are a reflection of what that shift looks like in practice. Four biosimilar denosumab products received approval as interchangeable in October 2025. Then, in November 2025, Poherdy (pertuzumab-dpzb), an antibody usually given with trastuzumab itself, was approved as the first interchangeable biosimilar in oncology. So where does this leave trastuzumab? The technical requirements case looks strong: analytical similarity, pharmacokinetic comparability and matched clinical efficacy and safety have all been demonstrated for approved products. Data switching is not necessary but its safety is supported by real-world cohorts from Sweden, Brazil and China. The unsettled is narrower: can a sponsor lean on data already sitting in an existing biologics license application, will oncology be judged by the same yardstick as the non-oncology cases so far, and how much will state-by-state differences in pharmacy substitution law blunt the real-world effect once a designation does land. The bottom line: the approval of pertuzumab brings the runway for trastuzumab interchangeability much closer than it looked even a year ago — although nothing is settled until a sponsor actually files and the FDA rules.