HERTHENA-PanTumor01: A global, multicohort, phase 2 trial of HER3-DXd in relapsed/refractory metastatic solid tumors.

TPS3164 Background: Human epidermal growth factor receptor 3 (HER3) is a member of the HER/EGFR family of receptor tyrosine kinases. HER3 is expressed in numerous solid tumors, including melanoma, head and neck squamous cell cancer (HNSCC), and gastric cancer, and high levels of HER3 expression in multiple tumor types are associated with poor clinical outcomes. HER3-DXd is a potential first-in-class HER3-directed antibody-drug conjugate (ADC) composed of a fully human anti-HER3 monoclonal antibody (patritumab) covalently linked to a potent topoisomerase I inhibitor payload via a tumor-selective cleavable linker. HER3-DXd has shown antitumor activity and a manageable safety profile in previously treated EGFR-mutated metastatic NSCLC and metastatic breast cancer. Based on clinical data and exposure-response analyses, HER3-DXd 5.6 mg/kg IV every 3 weeks (Q3W) was selected as the monotherapy dose for investigation in new indications. HERTHENA-PanTumor01 (NCT06172478) is a global, multicohort, open-label, single-arm, phase 2 trial evaluating the efficacy and safety of HER3-DXd in previously treated patients (pts) with cutaneous melanoma, HER2-negative gastric cancer, or HNSCC. Methods: Each cohort of HERTHENA-PanTumor01 will enroll 40 pts. Study sites are in Australia, Belgium, France, Japan, South Korea, Spain, Taiwan, the UK, and the US. Key inclusion criteria for melanoma include cutaneous or acral subtype, BRAF–wild-type or -mutant status, and progression on or after ≥1 anti–PD-(L)1 therapy. Key inclusion criteria for HNSCC include HPV+ or negative status and progression after platinum-based chemotherapy (PBC) ± anti–PD-(L)1 therapy; pts with nasopharyngeal cancer are excluded. Key inclusion criteria for gastric or gastroesophageal junction cancer include confirmed HER2-negative tumor status (immunohistochemistry IHC 0/1+ or IHC 2+/in situ hybridization negative) and progression after PBC ± anti–PD-(L)1 therapy; pts with HER2+ cancer are excluded. Other key exclusion criteria for all cohorts include any history of, suspected, or current interstitial lung disease; active brain metastases (treated/asymptomatic brain metastases are allowed); or prior treatment with an anti-HER3 antibody and/or ADC containing an exatecan derivative. A fresh biopsy or pretreatment archival biopsy performed since progression on or after treatment with the most recent cancer therapy is required for all cohorts. Pts will be treated with HER3-DXd 5.6 mg/kg IV Q3W; tumor assessments will occur every 6 wks for the first 48 wks, then every 12 wks until disease progression, adverse events, or other discontinuation criteria are met. The primary endpoint for each cohort is ORR by investigator per RECIST version 1.1. Secondary endpoints include safety and tolerability, DOR, DCR, PFS, overall survival, pharmacokinetics, and the correlation between HER3 IHC protein expression and efficacy. Clinical trial information: NCT06172478 .