Approximately 663 participants (at least 18 years) in approximately 200 study centers and in approximately 30 countries will be randomized with histologically or cytologically confirmed metastatic gastric or gastroesophageal junction adenocarcinoma. Participants must have received at least one cycle of first line therapy with any platinum/fluoropyrimidine doublet with or without anthracycline (epirubicin or doxorubicin) and must have discontinued this therapy prior to study entry due to disease progression.