Last updated: July 7, 2026
Ziihera (zanidatamab, ZW25) is a HER2-targeted biparatopic bispecific antibody — originated by Zymeworks, marketed by Jazz Pharmaceuticals (US) and BeiGene (other regions). It is FDA-approved (November 20, 2024) for previously-treated, unresectable or metastatic HER2-positive (IHC 3+) biliary tract cancer — the first HER2-targeted therapy approved specifically for biliary cancer. Given by IV infusion.
Mechanism of action:Unlike trastuzumab (which binds one HER2 epitope), zanidatamab binds two non-overlapping HER2 epitopes simultaneously — ECD4 (the trastuzumab-binding region) and ECD2 (the pertuzumab/dimerization region). This biparatopic binding drives enhanced HER2 receptor clustering, internalization and downregulation, complement-dependent cytotoxicity, and antibody-dependent cellular cytotoxicity — a more complete HER2 blockade from a single molecule.
Regulatory status:FDA accelerated approval November 20, 2024 for previously-treated HER2-positive (IHC 3+) biliary tract cancer, based on the HERIZON-BTC-01 Phase 2b single-arm trial (ORR ~52%, median duration of response ~14.9 months). Gastric/GEJ (the HERIZON-GEA program) and HER2-positive breast cancer are investigational (Phase 3 trials ongoing). Not an antibody-drug conjugate — no interstitial-lung-disease boxed warning; standard HER2-antibody cardiac (LVEF) monitoring applies.
For most of the last two decades, HER2-targeted therapy meant trastuzumab (Herceptin) and its relatives — antibodies that grab a single spot on the HER2 protein. Zanidatamab is different: it's biparatopic, grabbing two different spots on HER2 at once. Latching onto two epitopes pulls HER2 receptors into tight clusters, forces them off the cell surface, and recruits the immune system more effectively — a deeper HER2 shutdown from one molecule.
The biliary breakthrough. The headline is biliary tract cancer (which includes cholangiocarcinoma and gallbladder cancer). HER2 is amplified or overexpressed in roughly 5–20% of biliary cancers, and until recently there was no HER2-targeted option approved for it — patients who progressed after first-line gemcitabine-cisplatin plus durvalumab had few choices. In HERIZON-BTC-01, zanidatamab produced responses in about half of previously-treated HER2-positive patients, leading to the first-ever FDA approval of a HER2 therapy for biliary cancer in November 2024. A first-line Phase 3 is now recruiting.
Beyond biliary. Zanidatamab is being pushed across the HER2-positive map — gastric / gastroesophageal junction cancer (the HERIZON-GEA program, going head-to-head with the trastuzumab + chemo standard), HER2-positive breast cancer (including a Phase 3 and a combination with the HER2 pill tucatinib), colorectal, and bladder. HER2 status by IHC/ISH is the gating biomarker throughout.
HER2-Positive (IHC 3+) Previously-Treated Biliary Tract Cancer (HERIZON-BTC-01)
★ Biparatopic: Two HER2 Epitopes, One Antibody
Zanidatamab's distinctive feature is biparatopic binding — a single antibody molecule engages two separate HER2 epitopes (ECD2 + ECD4) at the same time. Trastuzumab binds only ECD4; pertuzumab only ECD2; the historical way to hit both was to give the two antibodies together. Zanidatamab does it in one molecule, producing tighter HER2 receptor clustering and more efficient receptor removal from the cell surface than a single-epitope antibody.
It is not an antibody-drug conjugate: it carries no chemotherapy payload and none of the interstitial-lung-disease (ILD) risk of the deruxtecan-platform HER2 ADCs like T-DXd (Enhertu). That makes it a mechanistically distinct HER2 tool — complementary to, not a replacement for, HER2 ADCs and the HER2 TKI tucatinib.
Curated set of recruiting / not-yet-recruiting interventional zanidatamab trials in the ClinTrialFinder corpus as of July 2026 (16 total), grouped by cancer. The pivotal HERIZON-BTC-01 trial has completed enrollment and is not listed here.
The HER2 toolbox now has several mechanistically distinct classes: single-epitope antibodies (trastuzumab, pertuzumab), the biparatopic bispecific antibody (zanidatamab), HER2 antibody-drug conjugates (T-DXd / Enhertu, which delivers a chemo payload and is a leading option in many HER2 settings), and the HER2 TKI tucatinib (an oral pill). Zanidatamab's niche is defined by (1) its first-in-class approval in HER2-positive biliary cancer, where it filled a genuine gap, and (2) its ADC-free profile (no ILD boxed warning), making it combinable with chemo, immunotherapy, or tucatinib. For the cross-cancer HER2-ADC view see the HER2 ADCs mechanism hub.
Zanidatamab's safety profile is characteristic of HER2-targeted antibodies (not ADCs): infusion-related reactions, diarrhea, and the HER2-class requirement for baseline and periodic cardiac monitoring (left-ventricular ejection fraction, LVEF) — because HER2 is expressed in heart muscle. Because it carries no chemotherapy payload, it does not have the interstitial-lung-disease boxed warning associated with the deruxtecan-platform HER2 ADCs. As with all HER2 therapy, HER2 status must be confirmed (IHC 3+ / ISH) before treatment.
What is Ziihera (zanidatamab) and how does it work?
Ziihera (zanidatamab, ZW25) is a HER2-targeted biparatopic bispecific antibody: unlike trastuzumab (one HER2 epitope), it binds two HER2 epitopes at once (ECD4 + ECD2), driving stronger HER2 clustering, internalization, and immune-mediated killing. IV infusion. Zymeworks-originated; marketed by Jazz Pharmaceuticals (US) and BeiGene.
What is Ziihera FDA-approved for?
FDA accelerated approval (Nov 20, 2024) for previously-treated, unresectable/metastatic HER2-positive (IHC 3+) biliary tract cancer, based on HERIZON-BTC-01 (ORR ~52%) — the first HER2 therapy approved for biliary cancer. Gastric/GEJ and breast are investigational (Phase 3 ongoing).
How is zanidatamab different from trastuzumab or T-DXd?
Trastuzumab = single-epitope HER2 antibody. T-DXd = HER2 antibody-drug conjugate (chemo payload; ILD boxed warning). Zanidatamab = biparatopic bispecific antibody (two epitopes, one molecule); NOT an ADC, no ILD boxed warning. Tucatinib = HER2 TKI pill. Complementary tools for different settings.
What cancers is zanidatamab being studied in?
HER2-positive biliary (approved + 1L Phase 3 NCT06282575), gastric/GEJ (HERIZON-GEA + pembrolizumab / paclitaxel-ramucirumab combos), HER2+ breast (Phase 3 NCT06435429, + tucatinib), colorectal, bladder, and HER2-expressing baskets. HER2 IHC/ISH status is the gating biomarker.
Does zanidatamab require heart monitoring?
Yes — like trastuzumab/pertuzumab, it can affect heart function (HER2 is in heart muscle), so baseline + periodic LVEF monitoring is standard. Common effects: infusion reactions, diarrhea. Not an ADC, so no interstitial-lung-disease boxed warning.
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