SUMMARY: The FDA on November 20, 2024, granted accelerated approval to Zanidatamab-hrii (ZIIHERA®), a bispecific HER2-directed antibody, for previously treated, unresectable or metastatic HER2-positive (IHC 3+) Biliary Tract Cancer (BTC), as detected by an FDA-approved test. The FDA simultaneously also approved VENTANA PATHWAY anti-HER-2/neu (4B5) Rabbit Monoclonal Primary Antibody as a companion diagnostic device to aid in identifying patients with BTC who may be eligible for treatment with Zanidatamab.
Biliary Tract Cancer (Cholangiocarcinoma) is a rare and highly aggressive heterogenous cancer and is the second most common type of primary liver cancer after Hepatocellular carcinoma. It comprises about 30% of all primary liver tumors and includes both intrahepatic and extrahepatic bile duct cancers. It is estimated that approximately 211,000 patients are diagnosed with Biliary Tract Cancer and 174,000 patients will die of the disease each year globally. Biliary Tract Cancer is most frequently diagnosed in patients between 50 to 70 years old, and 75% of patients are diagnosed at an advanced stage. BTCs consist of intrahepatic cholangiocarcinoma, extrahepatic cholangiocarcinoma, gallbladder cancer, and Ampulla of Vater cancer. Klatskin tumor is a type of Cholangiocarcinoma that begins in the hilum, at the junction of the left and right bile ducts. It is the most common type of Cholangiocarcinoma, accounting for more than half of all cases. About 8,000 people in the US are diagnosed with Cholangiocarcinoma each year and approximately 20% of the cases are suitable for surgical resection. Patients diagnosed with Biliary Tract Cancer have a very poor prognosis, and the 5-year survival among those with advanced stage disease is less than 10%, with limited progress made over the past two decades. There is therefore an urgent unmet need for new effective therapies. Patients with advanced Biliary Tract cancers often receive chemotherapy in the first and second line settings, with limited benefit. Gemcitabine and Cisplatin combination is currently the first line standard-of-care treatment.
BTCs are heterogenous and thus their pathogenesis and genomic drivers may vary. HER2 overexpression or gene amplification is one of the genomic drivers and HER2 overexpression rates vary depending on the anatomic origin of the Biliary Tract Cancer. Extrahepatic cholangiocarcinoma has a higher rate of HER2 overexpression (about 16-18%), compared to intrahepatic cholangiocarcinoma (about 5%), and about 10-16% for gallbladder cancers, making HER2 a potential therapeutic target in a vast majority of these patients.
Zanidatamab is a novel HER2-targeted, humanized, immunoglobulin G1 (IgG1), bispecific monoclonal antibody, that targets two distinct non-overlapping extracellular domains of HER2, ECD2 and ECD4 (biparatopic binding). This results in dual HER2 signal blockade, HER2 clustering, receptor internalization, and downregulation. This inhibits HER2 activation, HER2-mediated signaling and HER2-mediated tumor cell growth. The specific binding of Zanidatamab to tumor cells and HER2 aggregation also activates various immune-mediated responses, including Complement-Dependent Cytotoxicity (CDC), Antibody-Dependent Cellular Cytotoxicity (ADCC), and Antibody-Dependent Cellular Phagocytosis (ADCP) against tumor cells that overexpress HER2. Zanidatamab binds to HER2-expressing tumor cells with greater antibody saturation than Trastuzumab or Pertuzumab.
The present FDA approval was based on data from HERIZON-BTC-01 (NCT04466891), a pivotal Phase 2b, open-label, multicenter, single-arm trial, that evaluated the efficacy and safety of Zanidatamab in patients with HER2-positive BTC. This study included 87 patients with unresectable or metastatic HER2-positive BTC, and all patients received at least one prior Gemcitabine-containing regimen in the advanced disease setting. The median age was 64 years, 54% were women, 66% were Asian, 52% had gallbladder cancer, 30% had intrahepatic cholangiocarcinoma and 18% had extrahepatic cholangiocarcinoma. Patients received Zanidatamab at 20 mg/kg IV every two weeks in 28-day cycles.
Patients were assigned to one of two cohorts based on immunohistochemistry (IHC) status.
Cohort 1 (HER2-positive): Patients with IHC 3+ or IHC 2+ disease (N=80 total, including 62 with IHC 3+).
Cohort 2 (HER2-negative): Patients with IHC 0 or 1+ disease (N=7).
The major efficacy outcome measures were Objective Response Rate (ORR) and Duration of Response (DOR) as determined by an Independent Central Review.
Among the 62 patients with IHC3+ status per central assessment, the ORR was 52% and the median DOR was 14.9 months. The median Overall Survival was 18.1 months for IHC 3+ patients and 5.2 months for IHC 2+ patients. Common treatment related adverse events included diarrhea, infusion related reactions, nausea, vomiting, fatigue, and elevated liver enzymes. Treatment discontinuation rate was 2.3%.
In conclusion, the approval of Zanidatamab represents a significant advancement in the management of HER2-positive BTC and a critical unmet need. A Phase 3 trial is planned to evaluate Zanidatamab in the first-line setting for metastatic BTC.
Zanidatamab in previously-treated HER2-positive (HER2+) biliary tract cancer (BTC): Overall survival (OS) and longer follow-up from the phase 2b HERIZON-BTC-01 study. Pant S, Fan J, Oh D-Y, et al. J Clin Oncol. 2024;42(suppl 16):4091. doi:10.1200/JCO.2024.42.16_suppl.4091.
