Jazz Pharmaceuticals PLC (NASDAQ:JAZZ) saw its shares rise 1.5% in after-hours trading Wednesday following publication of expanded Phase 3 clinical trial data in the New England Journal of Medicine.
The paper reports detailed findings from the HERIZON-GEA-01 trial, which evaluated Ziihera (zanidatamab-hrii) combined with chemotherapy, with and without the anti-PD-1 antibody Tevimbra (tislelizumab), as a first-line treatment for adults with HER2-positive locally advanced or metastatic gastroesophageal adenocarcinoma.
The randomized study enrolled 914 patients across roughly 225 sites in more than 30 countries. According to the published results, both zanidatamab-containing regimens produced statistically significant improvements in progression-free survival when compared with the control arm of trastuzumab plus chemotherapy. Median progression-free survival was 12.4 months for the zanidatamab arms versus 8.1 months for the trastuzumab plus chemotherapy arm.
Overall survival data favored the zanidatamab combination that included tislelizumab. That regimen demonstrated a median overall survival of 26.4 months compared with 19.2 months for trastuzumab plus chemotherapy.
The NEJM publication also provided expanded subgroup analyses. These analyses indicated that the improvements in progression-free survival and overall survival were generally consistent across evaluated patient characteristics, including PD-L1 expression status, geographic region, and performance status.
Jazz noted that additional subgroup data, scheduled for presentation at the 2026 ASCO Annual Meeting, showed better outcomes with the zanidatamab-containing combinations irrespective of PD-L1 expression. The publication highlights that this included benefits observed in PD-L1-negative patients.
Specifically, in PD-L1-negative patients the combination of zanidatamab, tislelizumab, and chemotherapy was reported to provide prolonged survival versus the control arm. Among PD-L1-positive patients, median overall survival with the zanidatamab-containing combination was reported as 26.4 months compared with 21.2 months with trastuzumab plus chemotherapy.
Following the publication, Jazz has submitted the Phase 3 dataset to the National Comprehensive Cancer Network for potential inclusion in clinical practice guidelines. In parallel, a supplemental biologics license application for zanidatamab is under FDA Real-Time Oncology Review for the indication of first-line treatment of HER2-positive locally advanced or metastatic gastroesophageal adenocarcinoma.
These results and the regulatory activity reflect developments in oncology drug development and guideline adoption processes. Market reaction to the publication was modestly positive in extended trading, as investors absorbed the published efficacy gains and the company's regulatory progress.
Further subgroup detail to be presented at the 2026 ASCO Annual Meeting will provide additional context to the NEJM findings and may clarify how the observed benefits apply across clinical subpopulations.