A Phase III Open-label, Multicenter Trial of Maintenance Therapy With Avelumab (MSB0010718C) Versus Continuation of First-line Chemotherapy in Subjects With Unresectable, Locally Advanced or Metastatic, Adenocarcinoma of the Stomach, or of the Gastro-esophageal Junction

Maintenance Phase: Intravenous (IV) infusion (10 mg/kg over 1 hour) once every 2 weeks.

Induction Phase: Oxaliplatin was administered at a dose of 85 mg per square meter (mg/m\^2) as a continuous intravenous (IV) infusion on Day 1 along with leucovorin followed by 5-Fluorouracil every 2 weeks up to 12 weeks (or) Oxaliplatin at 130 mg/m\^2 IV on Day 1 along with capecitabine twice daily for 2 weeks followed by a 1-week rest period given every 3 weeks up to 12 weeks. Maintenance Phase: Participants were continued the same regimen of chemotherapy as they received during the Induction Phase until disease progression, significant clinical deterioration, unacceptable toxicity, or discontinuation.

Induction Phase: 5-Fluorouracil was administered at a dose of 2600 mg/m\^2 IV continuous infusion over 24 hours on Day 1 (or) 5-FU at 400 mg/m\^2 IV push on Day 1 and 2400 mg/m\^2 IV continuous infusion over 46-48 hours (Days 1 and 2) along with oxaliplatin and leucovorin every 2 weeks up to 12 weeks. Maintenance Phase: Participants were continued the same regimen of chemotherapy as they received during the Induction Phase until disease progression, significant clinical deterioration, unacceptable toxicity, or discontinuation.

Induction Phase: Leucovorin was administered at a dose of 200 mg/m\^2 IV (or) Leucovorin 400 mg/m\^2 IV on Day 1 along with oxaliplatin and 5-FU every 2 weeks up to 12 weeks. Maintenance Phase: Participants were continued the same regimen of chemotherapy as they received during the Induction Phase until disease progression, significant clinical deterioration, unacceptable toxicity, or discontinuation.

Induction Phase: Capecitabine was administered at a dose of 1000 mg/m\^2 twice daily for 2 weeks followed by a 1-week rest period given every 3 weeks along with oxaliplatin up to 12 weeks. Maintenance Phase: Participants were continued the same regimen of chemotherapy as they received during the Induction Phase every 3 weeks until disease progression, significant clinical deterioration, unacceptable toxicity, or discontinuation.

Treatment administered with the intent to maximize Quality of Life (QoL) without a specific antineoplastic regimen. These may include for example antibiotics, analgesics, antiemetics, thoracentesis, paracentesis, blood transfusions, nutritional support (including jejunostomy), and focal external-beam radiation for control of pain, cough, dyspnea, or bleeding. Best supportive care were administered per institutional guidelines and participants were visit the clinic every 3 weeks.

Induction Phase: Oxaliplatin will be administered at a dose of 85 mg per square meter (mg/m\^2) as a continuous intravenous (IV) infusion on Day 1 along with leucovorin followed by 5-Fluorouracil every 2 weeks up to 12 weeks (or) Oxaliplatin at 130 mg/m\^2 IV on Day 1 along with capecitabine twice daily for 2 weeks followed by a 1-week rest period given every 3 weeks up to 12 weeks.

Induction Phase: 5-Fluorouracil will be administered at a dose of 2600 mg/m\^2 IV continuous infusion over 24 hours on Day 1 (or) 5-FU at 400 mg/m\^2 IV push on Day 1 and 2400 mg/m\^2 IV continuous infusion over 46-48 hours (Days 1 and 2) along with oxaliplatin and leucovorin every 2 weeks up to 12 weeks.

Induction Phase: Leucovorin will be administered at a dose of 200 mg/m\^2 IV (or) Leucovorin 400 mg/m\^2 IV on Day 1 along with oxaliplatin and 5-FU every 2 weeks up to 12 weeks.

Induction Phase: Capecitabine will be administered at a dose of 1000 mg/m\^2 twice daily for 2 weeks followed by a 1-week rest period given every 3 weeks along with oxaliplatin up to 12 weeks.