This is an open-label, multicenter, phase II study. The purpose of this study is to evaluate the safety, tolerability and preliminary anti-tumor activity of SKB571 in participants with gastrointestinal tumors.

This is a multicenter, open-label, Phase II clinical study to evaluate the efficacy, safety, tolerability, PK characteristics, and immunogenicity of SKB571 in participants with gastrointestinal tumors. Approximately 120 subjects will be enrolled in this study, including 4 cohorts with approximately 20-30 participants enrolled in each cohort.

Inclusion Criteria:

1. Male or female, age ≥ 18 years and ≤ 75 years at the time of signing the informed consent form (ICF).
2. Participants must have histologically or cytologically confirmed gastrointestinal tumors.
3. At least one measurable lesion as assessed by the investigator according to RECIST v1.1.
4. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
5. Life expectancy ≥ 12 weeks as assessed by the investigator.
6. Adequate organ and bone marrow function.
7. Male and female participants must agree to use highly effective methods of contraception during the study treatment period.
8. Participants must voluntarily join this study, sign the ICF, and be able to comply with the visits and related procedures specified in the protocol.

Exclusion Criteria:

1. Participants with other malignant tumors within 3 years before the first dose of study treatment.
2. History or current metastases to central nervous system.
3. Current uncontrolled concomitant diseases
4. Clinically severe lung damage due to complications of lung disorder
5. Participants with a history of interstitial lung disease (ILD)/non-infectious pneumonitis
6. A history of severe skin diseases
7. Unresolved toxicity from prior anti-tumor therapy
8. Serious infection within 4 weeks before the first dose of study treatment
9. Known active pulmonary tuberculosis.
10. Participants who have undergone major surgery or had severe trauma within 4 weeks before the first dose, or are expected to require major surgery during the study.
11. Known history of allogeneic organ transplant or allogeneic hematopoietic stem cell transplant.
12. Pregnant or breastfeeding women.
13. Other conditions deemed by the investigator as unsuitable for participation in this clinical trial.