Efficacy and Safety of Patritumab Deruxtecan (HER3-DXd) in EGFR Inhibitor– Resistant, EGFR-Mutated Non–Small Cell Lung Cancer

Receptor tyrosine-protein kinase ERBB3 (HER3) is expressed in most EGFR-mutated lung cancers but is not a known mechanism of resistance to EGFR inhibitors. HER3-DXd is an antibody–drug conjugate consisting of a HER3 antibody attached to a topoisomerase I inhibitor payload via a tetrapeptide-based cleavable linker. This phase I, dose escalation/expansion study included patients with locally advanced or metastatic EGFR-mutated non–small cell lung cancer (NSCLC) with prior EGFR tyrosine kinase inhibitor (TKI) therapy. Among 57 patients receiving HER3-DXd 5.6 mg/kg intravenously once every 3 weeks, the confirmed objective response rate by blinded independent central review (Response Evaluation Criteria in Solid Tumors v1.1) was 39% [95% confi-dence interval (CI), 26.0–52.4], and median progression-free survival was 8.2 (95% CI, 4.4–8.3) months. Responses were observed in patients with known and unknown EGFR TKI resistance mechanisms. Clinical activity was observed across a broad range of HER3 membrane expression. The most common grade ≥3 treatment-emergent adverse events were hematologic toxicities. HER3-DXd has clinical activity in EGFR TKI–resistant cancers independent of resistance mechanisms, providing an approach to treat a broad range of drug-resistant cancers. SIGNIFICANCE: In metastatic EGFR-mutated NSCLC, after disease progression on EGFR TKI therapy, treatment approaches include genotype-directed therapy targeting a known resistance mechanism or chemotherapy. HER3-DXd demonstrated clinical activity spanning known and unknown EGFR TKI resistance mechanisms. HER3-DXd could present a future treatment option agnostic to the EGFR TKI resistance mechanism.