This is a multicenter, open-label Phase 1/2 study in participants with advanced solid tumors. The study consists of two parts: Part 1 is a dose-escalation phase to evaluate the safety and tolerability of ZGGS34 in advanced solid tumor participants; Part 2 is a cohort-expansion phase to assess the efficacy and safety of ZGGS34 (± chemotherapy) in selected MUC17-positive advanced solid tumor participants.

Inclusion Criteria:

• Fully understand the study and voluntarily sign the informed consent form;
• Male or female 18~75 years old.
• Archived tumor tissue within 24 months or fresh biopsy specimens must be provided for detection of MUC17 expression, and with positive MUC17 results required.
• Subjects in different study parts need to meet the following requirements:

Part 1: Dose Escalation Study：Histologically or cytologically confirmed advanced solid tumors who have failed standard treatment or no standard treatment available, or were intolerant to standard treatments.

Part 2: Cohort Expansion Study：Cohort 1 (Gastric cancer): Previously received at least one line systematic treatment and failed; HER2 status negative. Cohort 2 (Pancreatic cancer): Previously received at least one line systematic treatment and failed. Cohort 3 (Colorectal cancer): Previously received at least one line systematic treatment and failed; If patients with MSI-H/dMMR, prior PD-1 therapy is required. Cohort 4: Other patients with advanced solid tumors who have failed standard treatment or have no standard treatment available.

Exclusion Criteria:

• Patients having received any of the following treatments: Prior combination or sequential use of drugs targeting anti-MUC17 (including investigational drugs);Chemotherapy, immunotherapy, targeted therapy, endocrine therapy, and biological targeted medicines ≤ 4 weeks before the first dose. Local palliative radiotherapy and a small molecule targeted therapy ≤ 2 weeks before the first dose; Systemic immunosuppressive medications, such as corticosteroid within 14 days prior to the first dose; Use of any live or live attenuated vaccines against viral infections within 4 weeks of first dose.
• The investigator considers the subject unsuitable for enrollment in this clinical study for any other reason.