⁃ For all Parts:

• Metastatic or unresectable solid tumor.

• Histological or cytological documentation of a solid tumor via a pathology report.

• CLDN18.2-positive tumor sample defined as moderate-to-strong CLDN18.2 protein expression defined as intermediate (2+) to strong (3+) staining intensity in ≥ 50% of tumor cells as assessed by central testing using a CLIA-validated immunohistochemistry assay in formalin-fixed, paraffin-embedded (FFPE) neoplastic tissues. New biopsies and archival bio-samples are allowed. Bone biopsies are not allowed. Cytology specimens (including fine needle aspirates) will not be accepted for CLDN18.2 examination. If archival tissue samples from several points of time are available, the most recent one is preferred. Patients with a lower expression level or with CLDN18.2-negative cancers are not eligible.

⁃ Trial part-specific inclusion criteria:

⁃ For Part 1A: Patients with solid tumors, for which there is no available standard therapy likely to confer clinical benefit, or the patient is not a candidate for such available therapy. Patients must have received all available standard therapies and failed at least first-line standard of care therapy prior to enrolment. Measurable or evaluable disease per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1. Eligible tumor types are gastric cancer, GEJ and esophageal adenocarcinoma, pancreatic, biliary tract (cholangiocarcinoma and gallbladder cancer), and mucinous ovarian cancers. Additionally, patients with specific tumors (including colorectal cancer, non small-cell lung cancer, gastric subtype of endocervical adenocarcinoma) where there is scientific evidence that the CLDN18.2 could be elevated can be tested for CLDN18.2 expression.

⁃ For Part 1B: Patients with advanced pancreatic adenocarcinoma or cholangiocarcinoma who are eligible for treatment with nab-paclitaxel and gemcitabine. Measurable or evaluable disease per RECIST 1.1.