The U.S. Food and Drug Administration (FDA) has granted accelerated approval to zanidatamab (Ziihera) for the treatment of adults with unresectable or metastatic HER2-positive biliary tract cancer (BTC) who have previously undergone gemcitabine-based chemotherapy. This approval marks a significant advancement in the treatment landscape for this aggressive cancer, offering a new targeted therapy option for patients with limited alternatives.
Mechanism of Action
Zanidatamab is a first-in-class HER2-targeted antibody that uniquely binds to two distinct epitopes of the HER2 receptor. This dual binding mechanism not only inhibits HER2 signaling, thereby impeding tumor growth, but also promotes antibody-dependent cellular cytotoxicity (ADCC), enhancing the body's immune response against cancer cells. This multifaceted approach distinguishes zanidatamab from other HER2-targeted therapies.
Clinical Trial Results
The FDA's approval was based on the results of a clinical trial involving 62 patients with advanced HER2-positive BTC who had previously been treated with gemcitabine-based chemotherapy. The study demonstrated a 52% objective response rate (ORR) in patients treated with zanidatamab. The median duration of response (DOR) was approximately 15 months, indicating a sustained benefit from the treatment. These results highlight the potential of zanidatamab to provide meaningful clinical benefit in a patient population with limited treatment options.
Companion Diagnostic
In conjunction with the approval of zanidatamab, the FDA also approved the Ventana Pathway anti-HER-2/neu (4B5) Rabbit Monoclonal Primary Antibody, a companion diagnostic test designed to identify patients with HER2-positive tumors. This test is crucial for determining eligibility for zanidatamab treatment, ensuring that the therapy is directed towards patients most likely to benefit.
Safety and Warnings
The FDA's approval statement includes a warning regarding potential harm to unborn babies. Jazz Pharmaceuticals, the manufacturer of Ziihera, advises patients of reproductive potential to use effective contraception during treatment. Common side effects associated with zanidatamab include diarrhea, infusion-related reactions, stomachache, and fatigue.
Ongoing Research
Jazz Pharmaceuticals is currently evaluating zanidatamab in combination with standard therapy as a first-line treatment for HER2-positive BTC. The continued approval of zanidatamab is contingent upon the confirmation of clinical benefit in this ongoing trial. This research aims to further establish the role of zanidatamab in the treatment paradigm for HER2-positive biliary tract cancer.
