This is a Phase I, open-label, multi-center, first-in-human (FIH) clinical trial designed to evaluate the safety, tolerability, pharmacokinetic (PK) profiles, and the preliminary antitumor activity of JSKN021 in advanced malignant solid tumors.

Inclusion Criteria:

1. Voluntarily participate and sign the informed consent form.
2. Age ≥ 18 and ≤ 75 years old, male or female.
3. Eastern Cooperative Oncology Group performance status (ECOG PS) score of 0 or 1.
4. Expected survival ≥ 3 months.
5. Histologically or cytologically confirmed malignant solid tumors confirmed by histology and/or cytology, who have failed previous standard treatment (disease progression), are intolerant to standard treatment, or have no access to standard treatment.
6. At least one measurable lesion at baseline according to RECIST 1.1 criteria.
7. Adequate organ function.
8. Female subjects of childbearing potential or male subjects whose partners are of childbearing potential agree to use effective contraceptive measures.
9. Female subjects of childbearing potential must have a negative serum/urine pregnancy test within 7 days before the first dose.
10. Be able and willing to comply with the visits, treatment plans, laboratory tests, and other study-related procedures specified in the study protocol.
11. Adequate washout period of previous therapy before the first dose.

Exclusion Criteria:

1. Complicated with other malignant tumors within 3 years before the first dose.
2. History of brainstem, meningeal metastasis, spinal cord metastasis or compression, or carcinomatous meningitis; presence of active brain metastasis.
3. Screening imaging shows tumor invasion, compression, or occurrence in surrounding important organs or risk of esophagotracheal fistula or esophagopleural fistula.
4. Presence of clinically severe respiratory impairment caused by pulmonary disease complications.
5. Presence of the risk factors related to interstitial lung disease (ILD) or non-infectious pneumonia:
6. Presence of cardiovascular and cerebrovascular diseases or cardiovascular and cerebrovascular risk factors.
7. Uncontrolled infection.
8. Received live vaccines within 28 days before the first dose, or plan to receive live vaccines during the study period.
9. Toxicity of previous anti-tumor treatment has not fully or partially recovered.
10. Known allergy to any component of the study drug, or history of severe allergic reactions to other antibody drugs.
11. Pregnant and/or lactating women, or planning to become pregnant during the study period.
12. Known history of mental illness, substance abuse, alcoholism, etc., or other situations that the investigator deems may affect the safety or compliance of the study drug treatment.

No individual participant data will be shared. The informed consent form does not include provisions for sharing de-identified participant-level data with researchers outside the study team.