Ziihera® (zanidatamab-hrii) Combinations Achieve Unprecedented Results in First-Line HER2+ Locally Advanced or Metastatic GEA Including More Than Two Years Median Overall Survival Benefit

Rhea-AI Summary

Jazz Pharmaceuticals (Nasdaq: JAZZ) reported positive Phase 3 HERIZON-GEA-01 results for Ziihera (zanidatamab-hrii) in first-line HER2+ locally advanced or metastatic GEA. Both Ziihera arms (with chemotherapy, and with tislelizumab plus chemotherapy) showed ~35% reduction in progression or death versus trastuzumab plus chemotherapy, with median PFS >1 year (~12.4 months vs 8.1 months).

The Ziihera+tislelizumab arm reached a median overall survival of 26.4 months (OS HR 0.72; P=0.0043), a >7-month improvement versus control; Ziihera+chemo showed median OS 24.4 months (OS HR 0.80; P=0.0564) with a strong positive trend. Safety was consistent with HER2 and immunotherapy profiles; higher Grade ≥3 TRAEs and diarrhea rates were reported with the combination including tislelizumab.

Positive

• PFS improved to 12.4 months from 8.1 months (control)
• OS 26.4 months with Ziihera+tislelizumab (median)
• OS HR 0.72 (P=0.0043) for Ziihera+tislelizumab
• Durable responses: DoR 20.7 months with triplet arm
• 18-month PFS rate 43.9% with Ziihera+tislelizumab

Negative

• Higher Grade ≥3 TRAEs: 71.8% with Ziihera+tislelizumab
• Increased discontinuations due to AEs: 11.9% with triplet
• Higher Grade ≥3 diarrhea: 24.5% with triplet arm

News Market Reaction – JAZZ

-4.24%

10 alerts

-4.24% News Effect

-$446M Valuation Impact

$10.08B Market Cap

0.4x Rel. Volume

On the day this news was published, JAZZ declined 4.24%, reflecting a moderate negative market reaction. Our momentum scanner triggered 10 alerts that day, indicating notable trading interest and price volatility. This price movement removed approximately $446M from the company's valuation, bringing the market cap to $10.08B at that time.

Data tracked by StockTitan Argus on the day of publication.

Key Figures

Median PFS control: 8.1 months Median PFS Ziihera + chemo: 12.4 months Median OS Ziihera + tisl + chemo: 26.4 months +5 more

8 metrics

Median PFS control 8.1 months Trastuzumab plus chemotherapy arm in HERIZON-GEA-01

Median PFS Ziihera + chemo 12.4 months Ziihera plus chemotherapy arm in HERIZON-GEA-01

Median OS Ziihera + tisl + chemo 26.4 months Ziihera plus tislelizumab and chemotherapy arm in HERIZON-GEA-01

OS hazard ratio 0.72 OS HR (95% CI 0.57–0.90) vs trastuzumab plus chemotherapy

Objective response rate 70.7% ORR for Ziihera plus tislelizumab and chemotherapy

Median DoR 20.7 months Duration of response for Ziihera plus tislelizumab and chemotherapy

Grade ≥3 TRAEs 71.8% Ziihera plus tislelizumab and chemotherapy arm

30-month OS rate 43.8% Ziihera plus tislelizumab and chemotherapy arm

Market Reality Check

Price: $172.19 Vol: Volume 1,348,445 is 1.49x...

normal vol

$172.19 Last Close

Volume Volume 1,348,445 is 1.49x the 20-day average, indicating elevated interest ahead of the data presentation. normal

Technical Price at 174.39 is trading above the 200-day MA of 128.16, reflecting a pre-existing upward trend.

Peers on Argus

Peers show mixed moves, with names like TECH up and CORT and LEGN down, while on...

1 Up

Peers show mixed moves, with names like TECH up and CORT and LEGN down, while only MRNA appears in momentum scans. This points to a stock-specific catalyst for JAZZ rather than a broad biotech move.

Historical Context

5 past events · Latest: Dec 17 (Positive)

Pattern 5 events

Date	Event	Sentiment	Move	Catalyst
Dec 17	Investor events	Positive	-2.8%	Announcement of January 2026 investor webcasts including HERIZON-GEA-01 review.
Dec 09	Clinical data update	Positive	-4.0%	Presentation of Xywav DUET and sleep disorder data at major psychiatry meetings.
Dec 05	Clinical data update	Positive	+2.0%	Epidiolex real-world and clinical data presented at American Epilepsy Society meeting.
Dec 02	Clinical trial preview	Positive	+0.2%	Announcement that pivotal HERIZON-GEA-01 Ziihera results will be presented at ASCO GI.
Nov 18	Conference participation	Neutral	-2.5%	Participation in Citi’s 2025 Global Healthcare Conference and related webcast details.

Pattern Detected

Recent positive or neutral clinical and conference updates have often seen muted or negative next-day moves, suggesting limited immediate price follow-through on news.

Recent Company History

Over the last two months, Jazz has highlighted multiple R&D and investor-focused milestones. These include participation in investor conferences, extensive new data on Xywav and Epidiolex, and the announcement that full Phase 3 HERIZON-GEA-01 results for Ziihera would be presented at ASCO GI. The current detailed Ziihera Phase 3 readout builds directly on the November 17 8-K top-line disclosure and the December 2 preview of the ASCO GI presentation, reinforcing Jazz’s oncology pipeline narrative alongside its established sleep and epilepsy franchises.

Market Pulse Summary

This announcement details robust Phase 3 HERIZON-GEA-01 results for Ziihera combinations, including ...

Analysis

This announcement details robust Phase 3 HERIZON-GEA-01 results for Ziihera combinations, including median progression-free survival of 12.4 months and median overall survival up to 26.4 months, with benefits consistent across key subgroups. Prior disclosures previewed these data and underscored Jazz’s broader oncology and neuroscience portfolio. Investors may focus on durability of response, safety profiles such as Grade ≥3 adverse event rates, and how this program fits alongside existing revenue drivers and recent regulatory milestones when assessing long-term impact.

Key Terms

progression-free survival, overall survival, objective response rate, hazard ratio, +4 more

8 terms

progression-free survival medical

"prolongation of progression-free survival (PFS) with approximately 35% reduction"

Progression-free survival is the length of time during and after a treatment that a patient's disease does not get worse, measured from the start of treatment until the disease shows measurable signs of progression or the patient dies. Investors care because longer progression-free survival in clinical trials often signals that a drug is effective, improving chances of regulatory approval, market adoption, and revenue potential—think of it as a stopwatch showing how long a therapy can keep the illness at bay.

overall survival medical

"demonstrated a statistically significant and clinically meaningful overall survival (OS) benefit"

Overall survival is the average or median length of time patients remain alive after starting a treatment or entering a clinical study, measured regardless of cause of death. Investors care because it is a clear, hard measure of a therapy’s real-world benefit — like timing how long a new battery actually runs — and strong improvements in overall survival can drive regulatory approval, market adoption and revenue potential.

objective response rate medical

"Objective Response Rate (ORR) | 65.7 % | 69.6 % | 70.7 %"

The objective response rate (ORR) is the percentage of patients in a clinical trial whose tumors measurably shrink or disappear according to preset rules. Investors use it as a quick, objective signal of a drug’s ability to produce a clear treatment effect—like counting how many plants visibly respond after applying a new fertilizer—and higher ORR can improve odds of regulatory approval, commercial success, and company valuation.

hazard ratio medical

"PFS Hazard Ratio (HR) (95% CI) | — | 0.65 (0.52–0.81)"

A hazard ratio is a way scientists compare the chance of something happening over time between two groups, like patients taking different medicines. If the ratio is high, it means one group is more likely to experience the event sooner or more often, which helps determine how effective a treatment is or how risky a situation might be.

treatment-emergent medical

"Treatment-emergent diarrhea generally occurred early in treatment and resolved"

An observation or medical issue that appears or worsens after a patient starts a study treatment, used to identify side effects or safety signals tied to the treatment period. For investors, treatment-emergent findings reveal a drug’s real-world tolerability and can affect regulatory review, trial continuation or market adoption — think of it like noticing new problems only after switching to a new appliance, which influences whether people keep using it.

checkpoint inhibitor medical

"with or without the checkpoint inhibitor Tevimbra® (tislelizumab)"

A checkpoint inhibitor is a type of medicine that helps the immune system spot and attack cancer by blocking proteins that act like brakes on immune cells. For investors, these drugs matter because clinical trial results, regulatory approvals, safety profiles and market demand can quickly change a developer’s revenue and valuation; think of them as releasing the brakes on the immune system—potentially high reward but with safety and trial-risk consequences.

HER2-positive medical

"for adults with HER2-positive (HER2+) locally advanced or metastatic"

HER2-positive describes cancer cells that have too many copies of the HER2 gene or make too much of the HER2 protein, which acts like an overactive growth switch that drives tumor growth. For investors, HER2 status matters because it determines whether patients can receive specific, often expensive targeted therapies and diagnostic tests, so trial results, approvals, or competing drugs tied to HER2 can strongly affect drug sales and company value.

PD-L1 medical

"regardless of PD-L1 statusLate-breaking results to be presented"

PD-L1 is a protein found on the surface of some cells that acts like a stop sign for the immune system, telling certain immune cells to back off. It matters to investors because many cancer drugs and diagnostic tests target or measure PD-L1 to unlock immune responses or predict which patients will benefit, affecting clinical success, regulatory approval, and potential sales in the oncology market.

AI-generated analysis. Not financial advice.

Positive Phase 3 HERIZON-GEA-01 results support Ziihera as the HER2-targeted agent-of-choice in HER2+ first-line metastatic GEA and Ziihera plus chemotherapy to replace trastuzumab as the new standard of care, with or without tislelizumab regardless of PD-L1 status

Late-breaking results to be presented at the 2026 ASCO Gastrointestinal Cancers Symposium (ASCO GI) on January 8, 2026

For U.S. media and investors only

DUBLIN, Jan. 6, 2026 /PRNewswire/ -- Jazz Pharmaceuticals plc (Nasdaq: JAZZ) today announced  positive efficacy and safety results from the Phase 3 HERIZON-GEA-01 trial evaluating Ziihera^® (zanidatamab-hrii) in combination with chemotherapy, with or without the PD-1 inhibitor Tevimbra^® (tislelizumab), as first-line treatment for adults with HER2-positive (HER2+) locally advanced or metastatic gastroesophageal adenocarcinoma (GEA), including cancers of the stomach, gastroesophageal junction and esophagus.

The data will be presented as a late-breaking oral presentation at the 2026 ASCO Gastrointestinal Cancers Symposium (ASCO-GI) in San Francisco on January 8, 2026 from 8:57- 9:07 a.m. PST (abstract number: LBA285).

The study found:

• Both investigational arms, Ziihera plus tislelizumab and chemotherapy, and Ziihera plus chemotherapy, led to a statistically significant and clinically meaningful prolongation of progression-free survival (PFS) with approximately 35% reduction in the risk of disease progression or death versus trastuzumab plus chemotherapy. This resulted in a median PFS of more than one year, representing a greater than four-month improvement compared to the control arm.
• Ziihera plus tislelizumab and chemotherapy demonstrated a statistically significant and clinically meaningful overall survival (OS) benefit with a median OS of more than two years (26.4 months), the longest reported in a Phase 3 trial in GEA, representing a greater than seven-month improvement in median OS and a 28% reduction in the risk of death versus trastuzumab plus chemotherapy.
• At this first interim analysis, Ziihera plus chemotherapy showed a median OS of more than two years, with a strong trend toward statistical significance, favoring Ziihera plus chemotherapy versus trastuzumab plus chemotherapy. An additional planned OS interim analysis for Ziihera plus chemotherapy is currently expected in mid-2026.
• The OS and PFS benefits were generally consistent across major prespecified subgroups including geographic region and PD-L1 status for both investigational arms.

"Reaching more than two years of median overall survival in a global Phase 3 trial for HER2+ metastatic GEA is truly unprecedented," said Elena Elimova, M.D., Princess Margaret Cancer Centre, the presenting author of the late-breaking data. "The HERIZON-GEA-01 results represent the longest survival outcomes in a Phase 3 trial ever reported in this setting, with the zanidatamab plus tislelizumab and chemotherapy regimen improving median overall survival by more than seven months versus the control arm. The fact that both zanidatamab plus chemotherapy and zanidatamab plus tislelizumab and chemotherapy achieved median progression-free survival beyond one year further reinforces the depth and durability of benefit. These findings signal a meaningful step forward for patients who have historically faced very limited long-term outcomes."

"The results of the HERIZON-GEA-01 study are practice-changing," said Geoffrey Ku, M.D., associate attending physician on the Gastrointestinal Oncology Service in the Department of Medicine at Memorial Sloan Kettering Cancer Center and study co-author. "In addition to the progression-free survival and overall survival benefits, the remarkably long duration of response and consistent benefit across relevant subgroups, including PD-L1 positive and negative tumors, strongly suggest that zanidatamab plus chemotherapy, with or without tislelizumab, should become the new standard of care for patients with HER2+ first-line locally advanced unresectable or metastatic GEA."

Efficacy Summary from HERIZON-GEA-01

Primary Endpoints
Endpoint	Trastuzumab plus chemotherapy (control arm)	Ziihera plus chemotherapy	Ziihera plus tislelizumab and chemotherapy
Median PFS (95% confidence interval [CI])	8.1 months (7.0–8.9)	12.4 months  (9.8–14.5)	12.4 months (9.8–18.5)
PFS Hazard Ratio (HR) (95% CI)	—	0.65 (0.52–0.81) P<0.0001	0.63 (0.51–0.78) P<0.0001
Median OS (95% CI)	19.2 months (16.8–21.8)	24.4 months (20.4–30.0)	26.4 months (21.5–30.3)
OS HR (95% CI)	—	0.80 (0.64–1.01)*  P=0.0564	0.72 (0.57–0.90) P=0.0043
Key Secondary Endpoints
Endpoint	Trastuzumab plus chemotherapy (control arm)	Ziihera plus chemotherapy	Ziihera plus tislelizumab and chemotherapy
Objective Response Rate (ORR)	65.7 %	69.6 %	70.7 %
Median Duration of Response (DoR)	8.3 months	14.3 months	20.7 months
18-Month PFS Rate	20.9 %	38.0 %	43.9 %
30-Month OS Rate	30.0 %	42.2 %	43.8 %
Subgroup Findings	—	Consistent PFS benefit across PD-L1 status, geographic region, and ECOG performance status	Consistent PFS and OS benefit across PD-L1 status, geographic region, and ECOG performance status

* Did not reach statistical significance at the first interim OS analysis

The safety profile of Ziihera in combination with chemotherapy, with or without tislelizumab, was consistent with the known effects of HER2-directed therapy and immunotherapy, and no new safety signals were identified. Duration of treatment was longest on the Ziihera plus tislelizumab and chemotherapy arm. Rates of Grade ≥3 treatment-related adverse events (TRAEs) were 71.8% with Ziihera plus tislelizumab and chemotherapy, 59.0% with Ziihera plus chemotherapy, and 59.6% with trastuzumab plus chemotherapy. Discontinuations due to Ziihera- or trastuzumab-related and treatment discontinuations due to adverse events were 11.9% with Ziihera plus tislelizumab and chemotherapy, 8.5% with Ziihera plus chemotherapy, and 2.3% in the trastuzumab plus chemotherapy arm. The most common Grade ≥3 TRAE was diarrhea (24.5% of patients with Ziihera plus tislelizumab and chemotherapy; 20.0% with Ziihera plus chemotherapy; and 12.9% of patients in the trastuzumab plus chemotherapy arm). Importantly, discontinuation of either Ziihera or trastuzumab due to treatment-related diarrhea was uncommon (4.1% of patients with Ziihera plus tislelizumab and chemotherapy, 1.3% with Ziihera plus chemotherapy, and 0% of patients in the trastuzumab plus chemotherapy arm). Treatment-emergent diarrhea generally occurred early in treatment and resolved within three weeks. The manageable safety profile supports the feasibility of these combinations in the first-line metastatic setting.

"The strength of the HERIZON-GEA-01 data firmly positions Ziihera as the HER2-targeted agent-of-choice capable of reshaping first-line treatment for HER2+ metastatic GEA patients," said Rob Iannone, M.D., M.S.C.E., executive vice president, global head of research and development, and chief medical officer of Jazz Pharmaceuticals. "These results signal a clear evolution beyond the current standards and give us strong conviction as we move rapidly toward FDA submission. We are equally energized by the momentum we see across our broader development program, and we continue to evaluate Ziihera in multiple HER2-driven tumor types, including in HER2+ metastatic breast cancer with the ongoing Phase 3 EmpowHER-303 trial. This is the kind of scientific advancement that can redefine outcomes for patients, and we are committed to delivering it with urgency."

Jazz Pharmaceuticals will host an investor webcast on Friday, January 9, at 6:30 a.m. PT/9:30 a.m. ET to review the Ziihera data presented at the meeting. The webcast will include commentary from the company's senior management and Dr. Geoffrey Ku. The webcast may be accessed from the Investors section of the Jazz Pharmaceuticals website at www.jazzpharmaceuticals.com. To ensure a timely connection, it is recommended that participants register at least 15 minutes prior to the scheduled webcast. A replay of the webcast will be available via the Investors section of the Jazz Pharmaceuticals website.

About the Phase 3 HERIZON-GEA-01 Trial
HERIZON-GEA-01 (NCT05152147) is a global, randomized, open-label Phase 3 trial, conducted jointly with BeOne Medicines, to evaluate and compare the efficacy and safety of Ziihera plus chemotherapy, with or without tislelizumab, to trastuzumab plus chemotherapy as first-line treatment for adult patients with advanced/metastatic HER2+ GEA. The trial randomized 914 patients from approximately 300 trial sites in more than 30 countries. Appropriate patients for this trial had unresectable locally advanced, recurrent or metastatic HER2+ GEA (adenocarcinomas of the stomach or esophagus, including the gastroesophageal junction), defined as 3+ HER2 expression by IHC or 2+ HER2 expression by IHC with ISH positivity per central assessment. Patients were randomized to the three trial arms: Ziihera in combination with chemotherapy and tislelizumab; Ziihera in combination with chemotherapy; and trastuzumab plus chemotherapy. The trial is evaluating dual primary endpoints, PFS per blinded independent central review (BICR) and OS.

About Gastroesophageal Adenocarcinoma  
GEA, including cancers of the stomach, gastroesophageal junction, and esophagus, is the fifth most common cancer worldwide, and approximately 20% of patients have HER2+ disease.^1,2,3 HER2+ GEA has high morbidity and mortality, and patients are urgently in need of new treatment options. The overall prognosis for patients with GEA remains poor, with a global five-year survival rate of less than 30% for gastric cancer and about 19% for GEA.⁴

About Ziihera^® (zanidatamab-hrii)  
Ziihera (zanidatamab-hrii) is a bispecific HER2-directed antibody that binds to two extracellular sites on HER2. Binding of zanidatamab with HER2 results in internalization leading to a reduction in HER2 expression of the receptor on the tumor cell surface. Zanidatamab induces complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP). These mechanisms result in tumor growth inhibition and cell death in vitro and in vivo.⁵ In the United States, Ziihera is indicated for the treatment of adults with previously treated, unresectable or metastatic HER2-positive (IHC 3+) biliary tract cancer (BTC), as detected by an FDA-approved test.5 The U.S. FDA granted accelerated approval for this indication based on overall response rate and duration of response. Continued approval for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial(s).⁵ 

Zanidatamab is being developed in multiple clinical trials as a targeted treatment option for patients with solid tumors that express HER2. Zanidatamab is being developed by Jazz and BeOne under license agreements from Zymeworks, which first developed the molecule.   

The FDA granted Breakthrough Therapy designation for zanidatamab's development in patients with previously treated HER2 gene-amplified BTC, and two Fast Track designations for zanidatamab: one as a single agent for refractory BTC and one in combination with standard-of-care chemotherapy for first-line GEA. Additionally, zanidatamab has received Orphan Drug designations from the FDA for the treatment of BTC and GEA, as well as Orphan Drug designation from the European Medicines Agency for the treatment of BTC and gastric cancer.   

 Important Safety Information for ZIIHERA   

WARNING: EMBRYO-FETAL TOXICITY  Exposure to ZIIHERA during pregnancy can cause embryo-fetal harm. Advise patients  of the risk and need for effective contraception.

WARNINGS AND PRECAUTIONS 

Embryo-Fetal Toxicity 

ZIIHERA can cause fetal harm when administered to a pregnant woman. In literature reports, use of a HER2-directed antibody during pregnancy resulted in cases of oligohydramnios and oligohydramnios sequence manifesting as pulmonary hypoplasia, skeletal abnormalities, and neonatal death. 

Verify the pregnancy status of females of reproductive potential prior to the initiation of ZIIHERA. Advise pregnant women and females of reproductive potential that exposure to ZIIHERA during pregnancy or within 4 months prior to conception can result in fetal harm. Advise females of reproductive potential to use effective contraception during treatment with ZIIHERA and for 4 months following the last dose of ZIIHERA. 

Left Ventricular Dysfunction 

ZIIHERA can cause decreases in left ventricular ejection fraction (LVEF). LVEF declined by >10% and decreased to <50% in 4.3% of 233 patients. Left ventricular dysfunction (LVD) leading to permanent discontinuation of ZIIHERA was reported in 0.9% of patients. The median time to first occurrence of LVD was 5.6 months (range: 1.6 to 18.7). LVD resolved in 70% of patients. 

Assess LVEF prior to initiation of ZIIHERA and at regular intervals during treatment. Withhold dose or permanently discontinue ZIIHERA based on severity of adverse reactions. 

The safety of ZIIHERA has not been established in patients with a baseline ejection fraction that is below 50%. 

Infusion-Related Reactions 

ZIIHERA can cause infusion-related reactions (IRRs). An IRR was reported in 31% of 233 patients treated with ZIIHERA as a single agent in clinical studies, including Grade 3 (0.4%), and Grade 2 (25%). IRRs leading to permanent discontinuation of ZIIHERA were reported in 0.4% of patients. IRRs occurred on the first day of dosing in 28% of patients; 97% of IRRs resolved within one day. 

Prior to each dose of ZIIHERA, administer premedications to prevent potential IRRs. Monitor patients for signs and symptoms of IRR during ZIIHERA administration and as clinically indicated after completion of infusion. Have medications and emergency equipment to treat IRRs available for immediate use. 

If an IRR occurs, slow, or stop the infusion, and administer appropriate medical management. Monitor patients until complete resolution of signs and symptoms before resuming. Permanently discontinue ZIIHERA in patients with recurrent severe or life-threatening IRRs. 

Diarrhea 

ZIIHERA can cause severe diarrhea. 

Diarrhea was reported in 48% of 233 patients treated in clinical studies, including Grade 3 (6%) and Grade 2 (17%). If diarrhea occurs, administer antidiarrheal treatment as clinically indicated. Perform diagnostic tests as clinically indicated to exclude other causes of diarrhea. Withhold or permanently discontinue ZIIHERA based on severity. 

ADVERSE REACTIONS 

Serious adverse reactions occurred in 53% of 80 patients with unresectable or metastatic HER2-positive BTC who received ZIIHERA. Serious adverse reactions in >2% of patients included biliary obstruction (15%), biliary tract infection (8%), sepsis (8%), pneumonia (5%), diarrhea (3.8%), gastric obstruction (3.8%), and fatigue (2.5%). A fatal adverse reaction of hepatic failure occurred in one patient who received ZIIHERA. 

The most common adverse reactions in 80 patients with unresectable or metastatic HER2-positive BTC who received ZIIHERA (≥20%) were diarrhea (50%), infusion-related reaction (35%), abdominal pain (29%), and fatigue (24%). 

USE IN SPECIFIC POPULATIONS 

Pediatric Use 

Safety and efficacy of ZIIHERA have not been established in pediatric patients. 

Geriatric Use 

Of the 80 patients who received ZIIHERA for unresectable or metastatic HER2-positive BTC, there were 39 (49%) patients 65 years of age and older. Thirty-seven (46%) were aged 65-74 years old and 2 (3%) were aged 75 years or older. 

No overall differences in safety or efficacy were observed between these patients and younger adult patients. 

The full U.S. Prescribing Information for ZIIHERA, including BOXED Warning, is available at: https://pp.jazzpharma.com/pi/ziihera.en.USPI.pdf 

® TEVIMBRA (tislelizumab) is a registered trademark of BeOne Medicines.

Dr. Ku has financial interests related to Jazz Pharmaceuticals.

About Jazz Pharmaceuticals
Jazz Pharmaceuticals plc (Nasdaq: JAZZ) is a global biopharma company whose purpose is to innovate to transform the lives of patients and their families. We are dedicated to developing potentially life-changing medicines for people with serious diseases — often with limited or no therapeutic options. We have a diverse portfolio of marketed medicines, including leading therapies for sleep disorders and epilepsy, and a growing portfolio of cancer treatments. Our patient-focused and science-driven approach powers pioneering research and development advancements across our robust pipeline of innovative therapeutics in oncology and neuroscience. Jazz is headquartered in Dublin, Ireland with research and development laboratories, manufacturing facilities and employees in multiple countries committed to serving patients worldwide. Please visit www.jazzpharmaceuticals.com for more information. 

Cautionary Note Concerning Forward-Looking Statements 
This press release contains forward-looking statements, including, but not limited to, statements related to the potential therapeutic benefits of Ziihera and of combination therapies with Ziihera, Ziihera's potential as a new standard of care in HER2+ first-line GEA and other HER2-expressing cancers, expected timing of OS data from the pivotal Phase 3 HERIZON-GEA-01 and other statements that are not historical facts. These forward-looking statements are based on Jazz Pharmaceuticals' current plans, objectives, estimates, expectations and intentions and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties associated with the successful completion of regulatory activities and uncertain regulatory approval, risks related to failure or delays in successfully initiating or completing clinical trials and assessing patients and other risks and uncertainties affecting Jazz Pharmaceuticals and its development programs, including those described from time to time under the caption "Risk Factors" and elsewhere in Jazz Pharmaceuticals Securities and Exchange Commission filings and reports, including Jazz Pharmaceuticals' Annual Report on Form 10-K for the year ended December 31, 2024, as supplemented by Jazz Pharmaceuticals' Quarterly Report on Form 10-Q for the quarter ended September 30, 2025, and future filings and reports by Jazz Pharmaceuticals. Other risks and uncertainties of which Jazz Pharmaceuticals is not currently aware may also affect Jazz Pharmaceuticals' forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof or as of the dates indicated in the forward-looking statements, even if they are subsequently made available by Jazz Pharmaceuticals on its website or otherwise. Jazz Pharmaceuticals undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations or other circumstances that exist after the date as of which the forward-looking statements were made. 

Contacts:

Media Contact: 
Kristin Bhavnani
Head of Global Corporate Communications
Jazz Pharmaceuticals plc
CorporateAffairsMediaInfo@jazzpharma.com
Ireland +353 1 637 2141
U.S. +1 215 867 4948

Jazz Investor Contact: 
Jack Spinks 
Executive Director, Investor Relations 
Jazz Pharmaceuticals plc
InvestorInfo@jazzpharma.com
Ireland +353 1 634 3211
U.S. +1 650 496 2717

___________________________
¹ Abrahao-Machado I.F., et al. HER2 testing in gastric cancer: An update WorldJGastroenterol. 2016;22(19):4619-4625.
² Van Custem E., et al. HER2 screening data from ToGA: targeting HER2 in gastric and gastroesophageal junction cancer. Gastric Cancer. 2015;18(3):476-484.
³ Stroes, C.I., et al. A systematic review of HER2 blockade for the curative treatment of gastroesophageal adenocarcinoma: Successes achieved and opportunities ahead. CancerTreatRev. 2021;99:102249.
⁴ Battaglin F, et al. Molecular biomarkers in gastro-esophageal cancer: recent developments, current trends and future directions. Cancer Cell International. 2018;18(99).
⁵ ZIIHERA (zanidatamab-hrii) Prescribing Information. Palo Alto, CA: Jazz Pharmaceuticals, Inc.)

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FAQ

What were the median overall survival results for JAZZ Ziihera in HERIZON-GEA-01?

Median OS was 26.4 months for Ziihera+tislelizumab+chemo and 24.4 months for Ziihera+chemo versus 19.2 months for control.

How much did Ziihera improve progression-free survival versus trastuzumab in HERIZON-GEA-01 (JAZZ)?

Both Ziihera arms showed median PFS 12.4 months versus 8.1 months for trastuzumab+chemo, ~35% reduction in progression or death.

Did Ziihera plus tislelizumab meet statistical significance for overall survival (JAZZ, ASCO GI 2026)?

Yes. Ziihera+tislelizumab+chemo achieved OS HR 0.72 with P=0.0043 at the first interim analysis.

What safety risks should investors note from the JAZZ Ziihera HERIZON-GEA-01 results?

Higher rates of Grade ≥3 TRAEs (71.8%) and Grade ≥3 diarrhea (24.5%) were observed with Ziihera+tislelizumab+chemo versus control.

Will Ziihera change the standard of care for first-line HER2+ metastatic GEA (JAZZ)?

Investigators described the results as practice-changing, supporting Ziihera+chemo, with or without tislelizumab, as a potential new first-line standard based on PFS and OS gains.

When and where were the HERIZON-GEA-01 late-breaking results for JAZZ presented?

The data were presented as a late-breaking oral presentation at the 2026 ASCO Gastrointestinal Cancers Symposium on January 8, 2026 (abstract LBA285).