Erbitux in Combination With Xeloda and Cisplatin in Advanced Esophago-gastric Cancer

Inclusion Criteria:

* Written informed consent before any study-related activities are carried out
* Age greater than or equal to (\>=) 18 years
* Histologically confirmed adenocarcinoma of the stomach or gastroesophageal junction (Adenocarcinoma of the gastroesophageal junction \[AEG\] Types I-III according to Siewert classification)
* Archived tumor material sample for at least subsequent standardized Epidermal Growth Factor Receptor (EGFR) expression assessment
* Unresectable advanced (M0) or unresectable metastatic (M1) disease
* At least one radiographically documented measurable lesion in a previously non-irradiated area according to response evaluation criteria in solid tumors (RECIST). The primary tumor site is to be considered as a non-measurable lesion only
* Eastern Cooperative Oncology Group (ECOG) performance status 0-1
* Estimated life expectancy greater than (\>) 12 weeks
* Medically accepted contraception (if the risk of conception exists)
* Glomerular filtration rate (GFR) \>= 60 milliliter per minute (mL/min) The GFR is based on the Cockcroft-Gault formula for creatinine clearance
* Aspartate-aminotransferase (ASAT) less than or equal to (=\<) 2.5 \* upper limit of normal (ULN) and alanine-aminotransferase (ALAT) =\< 2.5 \*ULN
* Bilirubin =\< 3 \* ULN
* Absolute neutrophil count (ANC) \>= 1.5 \* 10\^9 per liter
* Platelets \>= 100 \* 10\^9 per liter
* Hemoglobin \>=10 gram per deciliter (g/dL) (without transfusions)
* Sodium and potassium within normal limits or =\< 10 percent above or below (supplementation permitted)

Exclusion Criteria:

* Prior chemotherapy, however, previous (neo-)adjuvant (radio-) chemotherapy allowed if finished \> 1 year prior to start of study treatment and no more than 300 mg/m\^2 cisplatin has been administered
* Prior treatment with an antibody or molecule targeting EGFR and/or Vascular Endothelial Growth Factor Receptor (VEGFR) related signaling pathways
* Brain metastasis and/or leptomeningeal disease (known or suspected)
* Radiotherapy (except localized radiotherapy for pain relief), major surgery or any investigational drug within 30 days before the start of study treatment
* Concurrent chronic systemic immune or hormone therapy not indicated in this study protocol (except for physiologic replacement)
* Clinically relevant coronary artery disease (New York Heart Association \[NYHA\] functional angina classification III/IV), congestive heart failure (NYHA III/IV), clinically relevant cardiomyopathy, history of myocardial infarction in the 12 months before study Screening, or high risk of uncontrolled arrhythmia
* Active Hepatitis B or C
* Chronic diarrhea or short bowel syndrome
* Presence of any contra-indication to treatment with cetuximab, capecitabine and cisplatin including:

  * Known hypersensitivity to capecitabine, fluorouracil, cisplatin, cetuximab or to any of the excipients of these drugs
  * Known dihydropyrimidine dehydrogenase (DPD) deficiency
  * Hereditary problems of galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption
  * Current treatment with sorivudine or chemically related analogues, such as brivudine
  * Symptomatic peripheral neuropathy National Cancer Institute - Common Terminology Criteria for Adverse Events (NCI-CTCAE) Grade \>= 2 and/or ototoxicity NCI CTCAE Grade \>= 2, except if due to trauma or mechanical impairment due to tumor mass
* Pregnancy or lactation period
* Concurrent treatment with a non-permitted drug
* Treatment in another clinical study within 30 days prior to study screening
* Previous malignancy other than gastric cancer within 5 years prior to study screening, except for basal cell cancer of the skin or pre-invasive cancer of the cervix
* Medical or psychological conditions that would not permit the subject to complete the study or sign informed consent
* Legal incapacity or limited legal capacity
* Significant disease which, in the Investigator's opinion, would exclude the subject from the study