Study of BGB-290 or Placebo in Participants With Advanced or Inoperable Gastric Cancer

This is a double-blind, placebo controlled, randomized multicenter global phase 2 study comparing the efficacy and safety of single agent poly (ADP-ribose) polymerase (PARP) inhibitor BGB-290 to placebo as maintenance therapy in participants with advanced gastric cancer who have responded to first line platinum based chemotherapy. Participants are randomized 1:1 to BGB-290 (Arm A) or placebo (Arm B). Randomization will be stratified by geography, biomarker status, and ECOG performance status.

Participants will undergo tumor assessments at screening and then every 8 weeks, or as clinically indicated. Administration of BGB-290 or placebo will continue until disease progression, unacceptable toxicity, death, or another discontinuation criterion is met.

After end of treatment, long-term follow-up assessments include tumor imaging every 8 weeks for those participants without disease progression, survival status, and new anticancer therapy.

Key Inclusion Criteria:

• Age ≥ 18 years.
• Signed informed consent.
• Histologically confirmed inoperable locally advanced or metastatic adenocarcinoma of the stomach or gastroesophageal junction.
• Received platinum based first line chemotherapy for ≤ 28 weeks.
• Confirmed partial response (PR) maintained for ≥ 4 weeks or complete response (CR).
• Able to be randomized to study ≤ 8 weeks after last platinum dose.
• Eastern Cooperative Oncology Group (ECOG) performance status ≤ 1.
• Adequate hematologic, renal and hepatic function.
• Must be able to provide archival tumor tissue for central biomarker assessment.
• Females of childbearing potential and non-sterile males must agree to use highly effective methods of birth control throughout the course of study and at least up to 6 months after last dosing.

Key Exclusion Criteria:

• Unresolved acute effects of prior therapy ≥ Grade 2.
• Prior treatment with PARP inhibitor.
• Chemotherapy, biologic therapy, immunotherapy or other anticancer therapy ≤ 14 days prior to randomization.
• Major surgery or significant injury ≤ 2 weeks prior to start of study treatment.
• Diagnosis of myelodysplastic syndrome (MDS)
• Other diagnoses of significant malignancy
• Leptomeningeal disease or brain metastasis
• Inability to swallow capsules or disease affecting gastrointestinal function.
• Active infections requiring systemic treatment.
• Clinically significant cardiovascular disease
• Pregnant or nursing females.

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