Abstract PS1-03-25: Incidence of hypersensitivity reactions in patients receiving trastuzumab biosimilars

Abstract Background: Currently multiple biosimilars of trastuzumab (Herceptin®) are approved for use in HER2-positive breast cancers. Accordingly, MD Anderson Cancer Center updated its formulary from trastuzumab (Herceptin®) to trastuzumab biosimilars: trastuzumab-qyyp (Trazimera®) and trastuzumab-anns (Kanjinti®), with trastuzumab-qyyp designated as the preferred agent. While these biosimilars have been approved based on extensive structural and functional characterization demonstrating similar clinical activity, differences in hypersensitivity reactions (HSRs) have been reported. We evaluated the incidence of HSRs in patients receiving trastuzumab biosimilars compared to the reference product. Methods: A retrospective chart review was conducted on patients who received trastuzumab products from January 1, 2019, to January 1, 2025. Patients with documented trastuzumab allergies in EMR were included in this analysis. Incidence of HSR between patients who received trastuzumab (Group A, n=612) and trastuzumab biosimilars (Group B, n=503) was compared. Results: HSRs were significantly more common in patients in patients who received trastuzumab biosimilars (Group B; n=86, 17.1%) compared to trastuzumab (Group A; n=22, 3.6%) (p