Zymeworks Inc. (NASDAQ:ZYME) saw its stock price soar 57% after unveiling encouraging topline findings from its Phase 3 HERIZON-GEA-01 study, which evaluated Ziihera (zanidatamab-hrii) as a first-line treatment for patients with HER2-positive gastroesophageal adenocarcinoma.
According to the company, pairing Ziihera with chemotherapy delivered a clinically meaningful and statistically significant improvement in progression-free survival compared to the regimen of trastuzumab plus chemotherapy. The combination also showed a meaningful benefit and a strong trend toward statistical significance in overall survival at the first interim analysis.
A second treatment arm, testing Ziihera with Tevimbra (tislelizumab) and chemotherapy, also outperformed the control group, demonstrating statistically significant gains in both overall survival and progression-free survival.
Following these results, Zymeworks’ development partner Jazz Pharmaceuticals plans to file a supplemental Biologics License Application in the first half of 2026 seeking approval to use Ziihera as a first-line therapy for HER2-positive locally advanced or metastatic gastroesophageal adenocarcinoma.
The safety findings were consistent with what is already known about Ziihera, chemotherapy, and Tevimbra, with no unexpected safety issues emerging.
Ziihera is already approved in the U.S., Europe, and China as a second-line treatment for biliary tract cancer, marketed through Jazz and BeOne Medicines. Jazz intends to present the new study results at a major medical conference in the first quarter of 2026.
Under its partnership agreements, Zymeworks remains eligible for additional regulatory and commercial milestone payments, as well as tiered royalties on future net sales of Ziihera.