Inclusion Criteria:

- Histologically confirmed adenocarcinoma of the stomach, the esophagus or the
gastroesophageal junction

- Inoperable locally advanced disease, resections with R0, R1 or R2 outcome or
metastatic disease.

- CLDN18.2 expression confirmed by immunohistochemistry in paraffin embedded tumor
tissue sample.

- Measurable and/or non-measurable disease as defined according to RECIST v1.1

- Age ≥ 18 years

- Written informed consent

- ECOG performance status (PS) 0-1

- Life expectancy > 3 months

Exclusion Criteria:

- Prior hypersensitivity reaction or intolerance to one of the compounds of the study
treatment

- Known HIV infection or known symptomatic hepatitis (A, B, C)

- Clinical symptoms of cerebral metastases

- Pregnancy or breastfeeding

- Patients treated with any bisphosphonate-based therapeutic for any indication during
the previous year

- Hypocalcemia that requires medication. Corrected (adjusted for serum albumin) serum
calcium < 8 mg/dl (2 mmol/L) or > 12 mg/dL (3.0 mmol/L)