Claudiximab is a monoclonal antibody specific for gastric and gastroesophageal adenocarcinomas. Preclinically, claudiximab was shown to inhibit tumor growth and to kill cancer cells by indirect (complement-dependent cytoxicity, antibody-dependent cellular cytotoxicity) and direct mechanisms (antiproliferative and proapoptotic effects). The aim of this phase I study is to establish safety, toxicity and maximal tolerable dose of a single infusion of claudiximab in patients suffering from relapsing, advanced gastroesophageal and gastric adenocarcinoma

Inclusion Criteria:

• Metastatic, refractory or recurrent disease of advanced gastroesophageal cancer (adenocarcinoma) proven by histology
• CLDN18.2 expression confirmed by immunohistochemistry
• Prior standard chemotherapy containing a fluoropyrimidine, a platinum compound and/or epirubicine, and - if clinically appropriate - docetaxel
• At least 1 measurable site of the disease according RECIST criteria (CT-scans or MRT not older than 6 weeks before study entry)
• Age ≥ 18 years
• ECOG performance status (PS) 0-1 or Karnofsky Index 70-100%
• Life expectancy > 3 months
• Platelet count ≥ 100,000/mm³
• Hemoglobin ≥ 10 g/dl
• INR < 1.5
• Bilirubin normal
• AST and ALT < 2.5 times upper limit of normal (ULN) (5 times ULN if liver metastases are present)
• Creatinine < 1.5 x ULN

Exclusion Criteria:

• Pregnancy or breastfeeding
• Prior allergic reaction or intolerance to a monoclonal antibody
• Prior inclusion in the present study
• Less than 3 weeks since prior anti-tumor or radiation therapy
• Other investigational agents or devices concurrently or within 4 weeks prior to this study
• Other concurrent anticancer therapies
• History of positive test for human immunodeficiency virus (HIV) antibody
• Known Hepatitis.
• Uncontrolled or severe illness.
• Concurrent administration of anticoagulation agents with vitamin K antagonists
• Concurrent administration of therapeutic doses of heparin (prophylactic doses are acceptable)

Access to anonymized individual participant level data will not be provided for this trial. Further details on Astellas' data sharing policy can be found at https://www.clinicaltrials.astellas.com/transparency/.