This is a multicenter, global, Phase 2, open-label, 2-part, first-line study to investigate the safety, tolerability, and anti-tumor activity of ZW25 (zanidatamab) plus standard first-line combination chemotherapy regimens for selected gastrointestinal (GI) cancers. Eligible patients include those with unresectable, locally advanced, recurrent or metastatic HER2-expressing gastroesophageal adenocarcinoma (GEA), biliary tract cancer (BTC), or colorectal cancer (CRC).

Part 1 of the study will first evaluate the safety and tolerability of ZW25 plus standard first-line combination chemotherapy (XELOX, FP, or mFOLFOX6 for GEA; mFOLFOX6 with or without bevacizumab for CRC; and CisGem for BTC) and will confirm the recommended dosage (RD) of ZW25 when administered in combination with each of these multi-agent chemotherapy regimens. Then, Part 2 of the study will evaluate the anti-tumor activity of ZW25 plus combination chemotherapy in HER2-expressing GEA, BTC, and CRC.

Inclusion:

• Disease diagnosis:

  • Part 1:
  • GEA: Unresectable, locally advanced, recurrent or metastatic HER2-expressing GEA (IHC 3+ or 2+ with or without gene amplification based upon local assessment or central assessment)
  • BTC: Unresectable, locally advanced, recurrent or metastatic HER2-expressing BTC (including intrahepatic cholangiocarcinoma [ICC], extrahepatic cholangiocarcinoma [ECC], or gallbladder cancer [GBC]) (IHC 3+ with or without gene amplification; or IHC 0, 1+ or 2+ with gene amplification, based upon central assessment)
  • CRC: Unresectable, locally advanced, recurrent or metastatic HER2-expressing CRC (IHC 3+ with or without gene amplification; or IHC 0, 1+ or 2+ with gene amplification, based upon central assessment). Patients will be required to be extended RAS (KRAS and NRAS) and BRAF wild-type based upon central assessment.
  • Part 2:
  • GEA: Unresectable, locally advanced, recurrent or metastatic HER2-expressing GEA (IHC 3+, or IHC 2+ and FISH+ by central assessment)
  • BTC: Same as Part 1
  • CRC: Same as Part 1

• Tumor measurements as per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1:

  • Part 1: Measurable or non-measurable disease
  • Part 2: Measurable disease

• An Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1

• Adequate organ function

• Adequate cardiac left ventricular function, as defined by a LVEF >/= institutional standard of normal

Exclusion:

• Prior treatment with a HER2-targeted agent

• Prior systemic anti-cancer therapy (including investigational products) except prior adjuvant/neoadjuvant therapy, which must be completed at least 6 months prior to first study treatment dosing. For subjects with BTC and CRC the following additional exceptions apply:

  • BTC: patients may have started therapy for advanced disease but may not have received more than one cycle of any standard gemcitabine-based chemotherapy regimen.
  • CRC: patients may have started therapy for advanced disease but may not have received more than one cycle of 5-FU-based chemotherapy (< 1 month of therapy).

• Patients with certain contraindications to bevacizumab cannot be enrolled on the mFOLFOX6-2 with bevacizumab arm.

• Palliative radiotherapy is allowed if completed at least 2 weeks prior to first study treatment dosing

• Untreated known brain metastases (patients with treated brain metastases who are off steroids, off antiseizure medications, and stable for at least 1 month at the time of screening are eligible)

• Clinically significant cardiac disease, such as ventricular arrhythmia requiring therapy, uncontrolled hypertension or any history of symptomatic congestive heart failure (CHF). Patients with known myocardial infarction or unstable angina within 6 months prior to randomization are also excluded.

• QTc Fridericia (QTcF) > 470 ms. For patients with longer QTcF on initial electrocardiogram (ECG), follow-up ECG may be performed in triplicate to determine eligibility

• Peripheral neuropathy > Grade 1 per NCI-CTCAE v5.0

• Clinically significant interstitial lung disease

• Prior or concurrent malignancy whose natural history or treatment has the potential to interfere with the safety or efficacy assessment of the investigational regimen

• Active hepatitis B or hepatitis C infection or infection with Human Immunodeficiency Virus (HIV)-1 or HIV-2 (Exception: patients with well controlled HIV [e.g., CD4 > 350/mm3 and undetectable viral load] are eligible)