Zymeworks Wins FDA Approval for Ziihera in HER2+ GEA

VANCOUVER, British Columbia – August 25, 2026

FDA Approval Expands First-Line HER2+ GEA Treatment Options

Zymeworks reported that Ziihera plus tislelizumab and fluoropyrimidine- and platinum-containing chemotherapy is approved for HER2-positive GEA patients with IHC 3+ or IHC 2+/ISH+ disease, regardless of PD-L1 status. Ziihera combined with fluoropyrimidine- and platinum-containing chemotherapy is also approved for patients with HER2-positive IHC 3+ GEA. The regulatory decision was supported by findings from the Phase 3 HERIZON-GEA-01 trial, which evaluated zanidatamab-based treatment in the first-line setting. According to the company, the regimen demonstrated a median overall survival of more than two years, representing an important development for patients with advanced HER2-positive disease. The approval broadens the potential population that can receive a zanidatamab-containing regimen and further establishes the asset within the treatment landscape for difficult-to-treat gastrointestinal cancers.

Ziihera Milestone Strengthens Zymeworks’ Partnered Oncology Strategy

The FDA decision also represents a significant commercial milestone for Zymeworks. Under its agreement with Jazz Pharmaceuticals, the approval triggers a $250 million milestone payment, bringing total upfront and milestone payments received from Jazz to $650 million. Zymeworks remains eligible for additional regulatory and commercial milestones of up to $1.3 billion, together with tiered royalties of 10% to 20% on net sales in Jazz’s licensed territories. Separately, its collaboration with BeOne Medicines provides eligibility for additional milestones and royalties in its licensed territories. This partnered model allows Zymeworks to participate in the commercial potential of zanidatamab while continuing to direct resources toward its wholly owned oncology pipeline, including next-generation trispecific T-cell engagers and antibody-drug conjugates (ADCs). The approval therefore has implications beyond Ziihera itself, strengthening the company’s broader strategy around licensed assets, recurring royalties and non-dilutive capital.supporting information for the company’s wider immunology and inflammation (I&I) development strategy.

Azymetric Platform Supports Continued Oncology Expansion

Ziihera was discovered and engineered by Zymeworks using its proprietary Azymetric™ bispecific antibody platform, which enables an antibody to bind two distinct epitopes on the same target protein. Zanidatamab targets HER2, a clinically established cancer target, and its development illustrates how Zymeworks has progressed an internally discovered molecule from research through clinical development before leveraging global pharmaceutical partners for commercialization. The company said the second FDA approval further validates its antibody engineering and development capabilities while potentially expanding zanidatamab’s reach across additional HER2-expressing solid tumors. HER2-positive GEA remains an area of substantial unmet medical need, particularly in advanced disease, and the latest approval adds another first-line treatment approach for eligible patients. With Jazz and BeOne continuing development activities in additional tumor types, Zymeworks is positioned to potentially generate further value from zanidatamab-related milestones and royalties while advancing its next-generation biotherapeutic programs. Zymeworks’ latest FDA milestone therefore marks both a regulatory achievement for Ziihera and an important business-development milestone for the company’s long-term oncology strategy.

Source: Zymeworks,press relese