...Age > 18 years (ethnical group: any; gender: female and male) Progression under or after one prior platinum-based or 5-fluoropyrimidine-based chemotherapy in metastatic disease At least four weeks from the last platinum-based or 5-fluoropyrimidin-based chemotherapy Histological proof of gastric adenocarcinoma including adenocarcinoma of the gastroesophageal junction with HER2 overexpression of the primary or metastatic tumor tissue determined by immunohistochemistry and FISH (Score IHC 3+ or Score IHC 2+ and FISH +) Metastatic (M1) or locally advanced disease At least one measurable lesion evaluable for response (RECIST criteria) Estimated life expectancy of > 3 months ECOG Performance Status: 0-2 Adequate cardiac function: LVEF > 50% (detected by echocardiogram) Absolute neutrophil count > 1,500/µl Absolute platelet count > 100,000 /µl Serum total bilirubin: < 2.0 x upper normal limit (UNL) Creatinine < 1.5 x UNL AST and ALT < 2.5 x UNL; < 5 x UNL in patients with documented liver metastases Alkaline phosphatase: < 2.5 UNL Negative pregnancy test Willingness to give written informed consent, written consent for data protection and willingness to participate and comply with the study...