FDA Clears Jazz's Ziihera for First-Line Stomach Cancer, Beating Herceptin's Decade-Long Reign

The FDA on Monday approved two new drug combinations built around Jazz Pharmaceuticals' bispecific antibody Ziihera (zanidatamab-hrii) for adults with HER2-positive advanced gastroesophageal adenocarcinoma, a cancer of the stomach, esophagus, and the junction between them. A treatment area that hasn't seen a new standard of care in more than ten years now has a new option.

The approval covers Ziihera paired with BeOne Medicines' Tevimbra (tislelizumab-jsgr) and chemotherapy for the full HER2-positive population, regardless of PD-L1 status, and a second regimen of Ziihera plus chemotherapy alone for a narrower subset. Zymeworks Inc. (Nasdaq: ZYME), the Vancouver biotech that discovered zanidatamab on its Azymetric antibody platform, licensed the drug to Jazz and stands to collect milestone payments and royalties.

The Data Behind the Approval

The approval rests on the Phase 3 HERIZON-GEA-01 trial, which randomized 914 patients across three arms. At a median follow-up of 25.9 months, median progression-free survival hit 12.4 months in both zanidatamab-containing arms, versus 8.1 months for trastuzumab (Herceptin) plus chemo, the decades-old standard.

The headline number is overall survival. Patients on Ziihera plus Tevimbra plus chemo lived a median of 26.4 months, versus 19.2 months on the trastuzumab combo, a 7.2-month improvement that FiercePharma's Angus Liu reported translates to a 28% reduction in risk of death (hazard ratio 0.72). That's the longest median overall survival reported in a Phase 3 trial in this disease setting, according to Jazz executive Rob Iannone in a PR Newswire release.

The Ziihera-plus-chemo-only arm posted a median OS of 24.4 months, but that difference against trastuzumab didn't reach statistical significance at the interim analysis, with a hazard ratio of 0.80 and a p-value of 0.06. Jazz says additional analyses are planned as the trial continues.

A subgroup breakdown mattered here too. Merck's Keytruda is already approved for HER2-positive gastric cancer, but only in tumors expressing PD-L1. FiercePharma noted the Ziihera-Tevimbra combo showed benefit in both PD-L1-positive and PD-L1-negative patients, with an even bigger effect in the PD-L1-negative group: median OS extended by 13.9 months to 29.7 months. That's the population Keytruda can't currently reach.

The Trade-off: More Diarrhea

This isn't a free upgrade. Grade 3 or higher adverse events hit 83.3% of patients on the Ziihera-Tevimbra-chemo combo, versus 73.8% on Ziihera-chemo and 74.5% on the trastuzumab standard.

Diarrhea drove much of that gap: 24.8% of patients on the triple combo experienced severe diarrhea, compared to 20.0% on Ziihera-chemo and 12.9% on the trastuzumab arm. The FDA's prescribing information for Ziihera carries boxed warnings for diarrhea and embryo-fetal toxicity, meaning it can harm a developing fetus.

A Legitimate Skepticism About Pharma Regulatory Trends, Applied to the Wrong Drug

A separate, unrelated FDA action this month drew sharp criticism. Writing in the Epoch Times, Jeffrey Tucker questioned the FDA's approval of a Moderna mRNA flu shot, arguing the company pooled data from three separate trials in a way that obscured the real-world benefit. Tucker calculated the shot's absolute risk reduction at just 0.8 percentage points, despite headline claims of "26.6 percent relative efficacy."

Tucker's broader point, that pharmaceutical companies and regulators increasingly compare new products against existing approved drugs rather than placebo, and that relative-risk percentages can make marginal gains look dramatic, is a legitimate critique of how efficacy claims get marketed to the public. Reasonable people should want absolute numbers, not just relative percentages, when weighing whether to take a drug.

But that critique applies to a flu vaccine trial, not to the Ziihera stomach-cancer approval. The GEA trial used a hard, unambiguous endpoint: death, measured in actual months of survival, not a "relative efficacy" percentage teased from thin infection-rate differences. A 7.2-month absolute gain in median overall survival, with a statistically significant hazard ratio, is a different category of evidence than a seasonal respiratory infection trial with low absolute case counts on both sides. Applying Tucker's skepticism of relative-risk framing to this cancer approval would be a mismatch, since Ziihera's core claim is measured in absolute months of life, not a squishy percentage.

What Happens Next

Jazz is targeting over $2 billion in peak sales for Ziihera across its approved indications, according to FiercePharma, which also noted doctors and analysts called the regimen "practice-changing" when the data was first presented at ASCO GI in January. The company hosted an investor webcast Monday at 4:30 p.m. ET to walk through the approval's commercial implications.

HERIZON-GEA-01 is still running, and Jazz says additional overall-survival analyses are planned for the Ziihera-chemo-only arm, where statistical significance hasn't yet been reached. Oncologists deciding which of the two newly approved regimens to prescribe, with or without Tevimbra, will be watching those follow-up numbers, along with real-world diarrhea rates outside the controlled trial setting.