Jazz's HER2 Drug Ziihera Shows Promise in Phase 3 Gastric Cancer Trial

Jazz Pharmaceuticals has announced positive results from its phase 3 HERIZON-GEA-01 trial, evaluating the efficacy of its HER2-targeted bispecific antibody, Ziihera (zanidatamab), in patients with HER2-positive gastroesophageal adenocarcinoma (GEA). The study, which compared Ziihera-based regimens to the current standard of care, has yielded results that Jazz describes as "practice changing."

Significant Improvements in Progression-Free and Overall Survival

The trial assessed two Ziihera-based regimens: a doublet combining Ziihera with chemotherapy, and a triplet adding BeOne Medicines' PD-1 inhibitor Tevimbra to the mix. Both regimens demonstrated notable benefits over the current standard treatment of Roche's Herceptin plus chemotherapy.

Patients receiving the Ziihera-chemotherapy doublet experienced a "clinically meaningful and statistically significant" improvement in progression-free survival (PFS) compared to the control arm. While overall survival (OS) data for this group showed a strong trend towards statistical significance, a follow-up analysis is expected next year.

The triplet regimen, however, produced even more impressive results, with "clinically meaningful and statistically significant improvements" in both PFS and OS. Importantly, these benefits were observed across PD-L1-positive and PD-L1-negative subgroups, potentially broadening the drug's applicability.

Regulatory Plans and Market Implications

Based on these encouraging results, Jazz Pharmaceuticals is preparing to submit a regulatory filing to the FDA in the first half of 2026. The company aims to seek approval for both the doublet and triplet regimens, positioning Ziihera as a potential new standard of care in first-line treatment for HER2-positive GEA.

Dr. Rob Iannone, Jazz's Chief Medical Officer, expressed confidence in the drug's potential impact, stating, "We believe these results will be practice changing, and highlight the potential impact of Ziihera for patients who are facing a devastating diagnosis and limited options in locally advanced or metastatic GEA."

The company also plans to work towards including these regimens in the National Comprehensive Cancer Network treatment guidelines, further solidifying Ziihera's position in the treatment landscape.

Financial and Strategic Implications

The positive trial results have had an immediate impact on the stock market, with Jazz's shares rising by approximately 20% in early trading following the announcement. Zymeworks, from whom Jazz licensed Ziihera in a 2022 deal, saw an even more dramatic increase of about 35% in its share price.

This phase 3 success bolsters Jazz's vision for Ziihera, which they believe could generate more than $2 billion in peak sales. The company had previously highlighted opportunities in HER2-positive stomach cancer and breast cancer as key drivers of this potential revenue.

The HERIZON-GEA-01 trial represents a significant milestone, being the first phase 3 study to demonstrate a benefit for a novel HER2-targeted therapy against a Herceptin-based combination in first-line HER2-positive GEA. This positions Jazz to potentially challenge the current treatment paradigm in this difficult-to-treat cancer type.