A Study to Evaluate the Safety and Tolerability of AB680 in Participants With Gastrointestinal Malignancies

Open to people ages 18 years and up

• Capable of giving signed informed consent
• Male or female participants ≥ 18 years of age at the time of screening
• Negative serum pregnancy test at screening and prior to dosing on Cycle 1 Day 1; negative serum or urine pregnancy test on the first day of each subsequent treatment period
• Histologically or cytologically confirmed metastatic pancreatic adenocarcinoma
• Naïve to any prior treatment, including chemotherapy, biological therapy, or targeted therapy for metastatic disease
  • Prior adjuvant therapy (including chemotherapy and/or radiotherapy) for pancreatic adenocarcinoma is permitted if neoadjuvant or adjuvant therapy was completed at least 6 months prior to study enrollment. Prior adjuvant therapy may include Nab- paclitaxel or gemcitabine
  • Participants initially diagnosed with locally advanced pancreatic cancer who have undergone chemotherapy then resection and had no evidence of disease are eligible if relapse of metastatic disease has occurred and if the last dose of chemotherapy was received more than 6 months before study entry
• Must have at least 1 measurable lesion per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. The measurable lesion must be outside of a radiation field if the participant received prior radiation
• Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1
• Confirmation that an archival tissue sample is available; if not, a new biopsy of a tumor must be obtained
• Immunosuppressive doses of systemic medications, such as corticosteroids or absorbed topical corticosteroids (doses > 10 mg/day prednisone or equivalent) must be discontinued at least 2 weeks (14 days) before investigational product administration. Physiologic doses of corticosteroids (≤ 10 mg/day of prednisone or its equivalent) or short pulses of corticosteroids (≤ 3 days) may be permitted
• Prior surgery that required general anesthesia or other major surgery as defined by the Investigator must be completed at least 4 weeks before investigational product administration
• Negative tests for hepatitis B surface antigen, hepatitis C virus antibody (or hepatitis C qualitative ribonucleic acid [RNA; qualitative]), and human immunodeficiency virus (HIV)-1 and HIV-2 antibody at screening
• Adequate organ and marrow function

• Use of any live attenuated vaccines against infectious diseases (eg, influenza, varicella) within 4 weeks (28 days) of initiation of investigational product
• Underlying medical conditions that, in the Investigator's or Sponsor's opinion, will make the administration of investigational product hazardous (eg, interstitial lung disease, active infections requiring antibiotics, recent hospitalization with unresolved symptoms
• Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial
• Any active autoimmune disease or a documented history of autoimmune disease or history of a syndrome that required systemic steroids or immunosuppressive medications, except for vitiligo or resolved childhood asthma/atopy. Participants with asthma who require intermittent use of bronchodilators (such as albuterol) will not be excluded from this study
• Prior malignancy active within the previous year except for locally curable cancers that have been apparently cured, such as basal or squamous cell skin cancer, superficial bladder cancer, or carcinoma in situ of the cervix, breast, or prostate cancer