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The FDA on Wednesday , a bispecific antibody, for pretreated HER2-positive biliary tract cancer.

Approval stipulates use in unresectable or metastatic cases, with HER2 positivity defined as an immunohistochemistry (IHC) score of 3+. According to drugmaker , the antibody binds to two extracellular sites on HER2, the first and only such drug FDA-approved for biliary tract cancer to do so.

Cohort 1 of the single-arm HERIZON-BTC-01 trial supported the approval. Among the 62 patients with unresectable or metastatic HER2-positive (IHC 3+) disease, zanidatamab monotherapy induced responses in 52%, with an estimated duration of response of 14.9 months. Complete responses occurred in 3.2%.

Patients in the open-label phase II trial had progressed on at least one gemcitabine-containing regimen and received zanidatamab intravenously every 2 weeks until disease progression or unacceptable toxicity.

"As a clinical investigator and medical oncologist focused on advancing the care of patients with biliary tract and liver cancers, I have experienced firsthand the significant unmet need for effective therapies for patients with these diseases," investigator James Harding, MD, of the Memorial Sloan Kettering Cancer Center in New York City, said in a press release from the drugmaker.

"Zanidatamab has demonstrated antitumor activity and is now a new option for patients with HER2-positive biliary tract cancer. I look forward to continued and successful drug development for patients with biliary tract cancer," added Harding.

As a condition of the accelerated approval, confirmation of benefit may be required. An ongoing global phase III trial () is currently evaluating first-line standard-of-care therapy with or without zanidatamab for patients with HER2-positive biliary tract cancer.

Zanidatamab comes with a boxed warning for embryo-fetal toxicity. also notes that left ventricular ejection fraction should be assessed prior to and at regular intervals during treatment, along with warnings and precautions about infusion-related reactions and diarrhea.

The most common adverse events (AEs) with zanidatamab in HERIZON-BTC-01 (≥20%) included diarrhea, infusion-related reactions, abdominal pain, and fatigue.

Serious AEs occurred in 53% of patients and included biliary obstruction (15%), biliary tract infection and sepsis (each in 8%), pneumonia (5%), diarrhea and gastric obstruction (each in 3.8%), and fatigue (2.5%). Permanent treatment discontinuation due to an AE occurred in 2.5% of patients. There was one fatal adverse reaction due to hepatic failure.

FDA also approved a companion diagnostic device from Ventana Medical Systems/Roche Diagnostics to identify eligible patients.

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