Data from Post Hoc Analysis of the Phase II DESTINY-PanTumor02 Study: Local and Central HER2 IHC Concordance and Trastuzumab Deruxtecan Efficacy by HER2 IHC Status in HER2-Expressing Solid Tumors

AbstractPurpose: Accurate HER2 status assessment is crucial to identify patients with HER2-expressing tumors. In this post hoc analysis of DESTINY-PanTumor02 (NCT04482309), we report concordance between local and central HER2 immunohistochemistry (IHC) results. Patients and Methods: This open-label, phase II study evaluated trastuzumab deruxtecan (T-DXd; 5.4 mg/kg once every 3 weeks) for HER2-expressing (IHC 3+/2+ by local or central testing) locally advanced, unresectable, or metastatic solid tumors after ≥1 systemic treatment or without alternative treatments. Results: In total, 267 patients received T-DXd; 75.7% were enrolled based on local test results. Concordance between local and central HER2 test results was 58.6% for IHC 3+, 54.5% for IHC 2+, and 73.4% for IHC 3+ and IHC 2+ tumors combined. Conclusions: The moderate concordance observed between local and central IHC testing in DESTINY-PanTumor02 highlights the need for a validated diagnostic test and standardized algorithm for HER2 status assessment in solid tumors to ensure appropriate patient identification for HER2-directed therapies.