Investigation of the outcome of an adjuvant treatment with catumaxomab as compared to surgery alone in patients after curative resection of a gastric adenocarcinoma in order to gain more detailed information primary on safety, tolerability and feasibility and secondary on relevant efficacy parameters.

A controlled, randomized, open-label, multi-center, parallel-group, Phase II study to generate valid hypotheses on safety and efficacy issues in patients with a primary confirmed diagnosis of gastric adenocarcinoma and a high risk of disseminated tumor cells due to serosal infiltration after curative gastrectomy. Eligible patients will be centrally randomized by IVRS during operation to one of the two study groups in an 1:1 ratio: surgery plus catumaxomab or surgery alone.

Treatment with catumaxomab will consist of an initial dose of 10 µg given intraoperatively as an intraperitoneal bolus on day 0 and of four following ascending doses (10-20-50-150 µg) which will be administered as an i.p.-infusion via a provided indwelling catheter on the days 7, 10, 13 and 16, respectively.

Inclusion Criteria:

• Signed and dated informed consent
• Patient has a primary diagnosis of a histologically confirmed gastric adenocarcinoma (including GE junction Siewert-Type 2 or 3)
• Intended curative gastrectomy ('en-bloc´-R0-resection considering the standard D2-scheme)
• Serosal infiltration (T3/T4, N+/-, M0) confirmed by immediate section with histopathologic assessment during surgery
• Karnofsky index >= 70
• Negative pregnancy blood test at screening in women with childbearing potential

Exclusion Criteria:

• Presence of distant metastases
• Macroscopic and microscopic residual tumor present after surgery
• State after pancreas resection or thoracotomy
• Exposure to prior cancer therapy or planned adjuvant chemo-or radiotherapy of the current gastric cancer
• Previous treatment with non-humanized mouse or rat monoclonal antibodies
• Known/suspected hypersensitivity to catumaxomab or similar antibodies
• Any cancer disease or any cancer treatments within the last 5 years
• Presence of constant immunosuppressive therapy
• Inadequate renal function (creatinine > 1.5 x ULN)
• Inadequate hepatic function (AST or ALT > 2.5 x ULN or bilirubin >= 1.5 x ULN)
• Platelets < 75000 cells/mm³; absolute neutrophil count < 1500 cells/mm³
• Patient had a bowel obstruction within the last 30 days
• Pregnant or nursing woman, or woman of childbearing potential who is not using an effective contraceptive method during the study and at least contraceptives, intrauterine devices, double-barrier method, contraceptive patch, male partner sterilization or condoms)
• Presence of any acute or chronic systemic infection
• Any further condition which according to the investigator results in an undue risk to the patient during participating in the present study
• Patient is an employee of any involved study investigator or any involved institution including the study sponsor
• Parallel participation in another clinical trial or previous participation in this study
• Treatment with another investigational product during this study or during the last 30 days prior to study start