Jazz Pharmaceuticals’ Ziihera Trial Rocks the Market—A New Era in Oncology?

In a week dominated by biotech headlines, few announcements carried more weight than the positive Phase 3 data for Ziihera, the HER2-targeted bispecific antibody developed by Jazz Pharmaceuticals and Zymeworks. On November 18, 2025, Jazz Pharmaceuticals reported that the HERIZON-GEA-01 trial of Ziihera (zanidatamab) in first-line treatment of HER2-positive gastroesophageal adenocarcinoma (GEA) had met its endpoints, driving strong progression-free survival and overall survival results. This milestone marks a significant leap in treatment options for one of the world’s most aggressive and deadly cancers. The announcement sparked a sharp rally in both Jazz and Zymeworks’ stock prices, fueled by renewed investor optimism and confidence in Ziihera’s clinical and commercial potential. Against a backdrop of cautious FDA receptivity and increasing demand for targeted oncology solutions, the trial results have sparked hope among physicians and patients alike while triggering a reevaluation of both companies’ strategic outlooks.