A Study of Herceptin (Trastuzumab) in Combination With Cisplatin/Capecitabine Chemotherapy in Participants With Human Epidermal Growth Factor Receptor 2 (HER2)-Positive Metastatic Gastric or Gastro-Esophageal Junction Cancer

Inclusion Criteria:

Histologically confirmed adenocarcinoma of the stomach or gastro-esophageal junction with metastatic disease documented to involve at least liver or lung or both
Measurable disease according to RECIST Version 1.1 or non-measurable evaluable disease
At least 2 organs involved in metastatic gastric tumor (including at least lung or liver or both) in addition to the site of primary tumor, where metastasis in distant lymph nodes, peritoneal metastasis, and malignant pleural effusion may count as "organs" in this context
HER2-positive primary or metastatic tumor as assessed by central laboratory
Adequate renal function (creatinine clearance greater than equal to (≥) 45 milliliters per minute [mL/min])
Eastern Cooperative Oncology Group (ECOG) performance status of 2

Exclusion Criteria:

Previous chemotherapy for locally advanced or metastatic disease
Prior gastrectomy (partial or total) for the underlying malignant disease under investigation
Prior therapy with an anti-HER2 agent and/or platinum-based chemotherapeutic agent
Residual relevant toxicity resulting from previous therapy
Lack of physical integrity of the upper gastrointestinal tract or malabsorption syndrome (such as jejunostomy probe and gastric or jejunostomy tubes) which may impair the ability to administer or absorb capecitabine
Current (significant or uncontrolled) gastrointestinal bleeding
Other malignancy within the last 5 years, except for carcinoma in situ of the cervix and basal or squamous cell carcinoma of the skin
History of documented congestive heart failure, angina pectoris requiring medication, electrocardiogram (ECG) evidence of transmural myocardial infraction, poorly controlled hypertension, clinically significant valvular heart disease, or high-risk uncontrollable arrhythmias
Baseline left ventricular ejection fraction (LVEF) less than (<) 50%, documented by echocardiography, multiple-gated radionuclide angiography (MUGA) scan, or cardiac magnetic resonance imaging (MRI)
Chronic or high-dose corticosteroid therapy
History or clinical evidence of brain metastases
Pregnant women
Active infection with human immunodeficiency virus (HIV), hepatitis B, or hepatitis C, or HIV-seropositive