The UK Medicines and Healthcare products Regulatory Agency (MHRA) has granted approval to zanidatamab (Ziihera, Jazz Pharmaceuticals) for the treatment of adults with advanced biliary tract cancer. 

The treatment was approved through the International Recognition Procedure (IRP), which allows the MHRA to rely on decisions by trusted international regulators.

The authorisation applies to patients whose tumours demonstrate high HER2 expression (immunohistochemistry [IHC] 3+) and who have progressed after at least one prior systemic therapy. It addresses an unmet need for patients with unresectable or metastatic disease for whom surgery is no longer feasible.

How the Bispecific Antibody Works

Zanidatamab is a bispecific antibody that employs a dual-binding strategy, attaching to two non-overlapping sites on the HER2 protein. This mechanism enhances receptor internalisation and effector cell recruitment, improving targeting of tumour cells with elevated HER2 expression.

Zanidatamab is administered by intravenous infusion every 2 weeks at a dose of 20 mg/kg of body weight.

What the Data Shows

The approval was based on data from the phase 2b HERIZON-BTC-01 trial, which included 80 patients with locally advanced or metastatic biliary tract cancer not amenable to surgery. The single-arm study evaluated zanidatamab in a treatment-resistant population without a placebo comparator.

Among the 62 patients with high HER2 levels, approximately 52% experienced tumour reduction or complete elimination after an average follow-up of 34 months. The confirmed objective response rate was 41.3% across all participants, with a median duration of response of 14.9 months.

In patients with IHC 3+ tumours, the response was 51.6%, with a median overall survival of 18.1 months.

Safety Profile and Next Steps

Zanidatamab demonstrated a manageable safety profile. Grade 3 treatment‑related adverse events were observed in 18% of patients, most commonly diarrhoea (5%) and decreased ejection fraction (3%). No grade 4 treatment‑related adverse events or treatment‑related deaths were reported. 

Full prescribing details, including contraindications and the complete adverse event profile, will be published on the MHRA’s website within 7 days of approval.