Study to Evaluate the Safety and Tolerability of Andecaliximab as Monotherapy and in Combination With Anti-Cancer Agents in Japanese Participants With Gastric or Gastroesophageal Junction Adenocarcinoma

Key Inclusion Criteria:

* Must have been born in Japan and must not have lived outside of Japan for a period \> 1 year in the 5 years prior to Day 1
* Must be able to trace their maternal and paternal ancestry of parents and grandparents as ethnically Japanese
* Histologically confirmed inoperable advanced gastric adenocarcinoma (including adenocarcinoma of the GEJ) or relapsed gastric adenocarcinoma
* Cohorts 1, 2, and 3: Human Epidermal Growth Factor Receptor 2 (HER2)-negative tumor (primary tumor or metastatic lesion). Enrollment in Cohort 4 is not restricted by HER2 status (adults with HER2-positive, HER2-negative, or unknown HER2 status are eligible)
* Cohort 1: Prior antitumor therapy or cytotoxic chemotherapy is acceptable. Individuals who are not eligible to receive standard treatments should enroll on the study.
* Cohorts 2 and 3: Prior antitumor therapy or cytotoxic chemotherapy for metastatic disease is not acceptable. Individuals must be chemo-naive in the metastatic setting
* Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 1
* Adequate baseline organ function (within 28 days prior to Day 1)
* Coagulation: International Normalized Ratio (INR) ≤ 1.5 (unless receiving anticoagulation therapy)
* For females of childbearing potential, willingness to use a protocol-recommended method of contraception from the screening visit throughout the study treatment period and for defined periods following the last dose of andecaliximab and/or anti-cancer agent(s)
* For males of childbearing potential having intercourse with females of childbearing potential, willingness to use a protocol-recommended method of contraception from the start of andecaliximab, throughout the study treatment period, and for protocol defined periods following the last dose of andecaliximab and/or anti-cancer agent(s)
* Willingness to comply with scheduled visits, drug administration plan, imaging studies, laboratory tests, other study procedures, and study restrictions
* In addition to the applicable criteria above, participants in Cohort 4 must meet additional inclusion criteria to be eligible for participation in this study:

  * Measurable gastric or GEJ adenocarcinoma
  * Must have progressed on at least 1 prior systemic therapy or line of treatment for unresectable/metastatic disease.
  * Activated partial thromboplastin (aPTT) ≤ 1.5 times the upper limit of normal
  * Thyroid function tests should be within normal limits.

Key Exclusion Criteria:

* History or evidence of a clinically significant disorder, condition, or disease that, in the opinion of the investigator and medical monitor would pose a risk to participant safety or interfere with the study evaluations, procedures, or completion
* Pregnant or lactating. Enrollment of lactating females after discontinuation of breastfeeding is not acceptable.
* Individuals with known central nervous system (CNS) metastases, unless metastases are treated and stable and the individual does not require systemic steroids
* Radiotherapy within 28 days of Day 1
* Myocardial infarction, symptomatic congestive heart failure (New York Heart Association Classification \> Class II), unstable angina, or serious uncontrolled cardiac arrhythmia within the last 6 months of Day 1
* History of major surgery within 28 days of Day 1
* Serious systemic fungal, bacterial, viral, or other infection that is not controlled or requires IV antibiotics
* Individuals known to be positive for human immunodeficiency virus (HIV), hepatitis C infection (per local standard diagnostic criteria), or acute or chronic hepatitis B infection (per local standard diagnostic criteria)
* In addition to the applicable criteria above, participants in Cohort 4 who meet any of the following exclusion criteria will not be enrolled in this study

  * Have received only neoadjuvant or adjuvant therapy for gastric adenocarcinoma
  * Prior treatment with anti-cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA-4) agents, anti-programmed cell death protein 1 (anti PD-1) or anti-programmed cell death ligand 1 (anti-PD-L1) agents, anti-programmed cell death ligand 2 (anti-PD-L2) agents, anti-matrix metalloprotease (anti-MMP) agents, or other immunomodulatory therapies

NOTE: Other protocol defined Inclusion/ Exclusion criteria may apply.