This is a multicenter, open-label, multiple-dose, FIH Phase 1/2a trial. The Phase 1 portion uses Bayesian optimal interval (BOIN) design to escalate and determine the MTD and/or RP2D with potential backfill cohorts. The Phase 2a portion consists of dose optimization followed by cohort expansion to confirm safety and tolerability and to further evaluate the efficacy of the selected RP2D in selected solid tumor malignancies for VBC108.

Inclusion Criteria:

1. The participant or the participant's legally acceptable representative is willing and able to provide a written ICF before initiating any trial procedure.
2. Histologically or cytologically confirmed unresectable advanced/metastatic solid tumor .
3. At least one measurable lesion as assessed by the investigator according to RECIST v1.1 criteria.
4. Male or female adults (defined as ≥ 18 years of age).
5. ECOG performance status 0-1.
6. Life expectancy greater than 12 weeks.
7. Archived tumor tissue sample available or able to undergo a fresh biopsy collection.
8. Adequate organ and bone marrow function.
9. Participants must meet the minimum washout period requirements before the first dose of investigational drug.

Exclusion Criteria:

1. Any unresolved toxicity of Grade ≥2 from previous anti-cancer treatment.
2. Known or suspected brain metastases, or spinal cord compression.
3. Prior treatment with an ADC targeting CLDN18.2x CDH17 bispecific ADC.
4. Prior treatment with any ADC carrying a topoisomerase I inhibitor (TOP1i) payload.
5. Prior treatment with CLDN18.2 targeting CAR-T.