A First-in-Human Study of YL217 in Patients With Advanced Solid Tumors

Inclusion Criteria:

• Informed of the study before the start of the study and voluntarily sign their nameand date in the ICF

• Able and willing to comply with protocol visits and procedures

• Age≥ 18 years

• ECOG PS of 0 or 1

• Tumor types as below:

For Part 1 and Part 2: Pathologically confirmed diagnosis of an advanced solid tumor.

For Part 3 (Histologically or cytologically confirmed diagnosis+ locally advanced unresectable or metastatic disease)

• Adequate organ and bone marrow function.

• Have at least 1 extracranial measurable tumor lesion.

• Adequate archival formalin-fixed paraffin embedded （FFPE） tissue from prior biopsy.

Exclusion Criteria:

• Prior treatment with an agent targeting CDH17

• Prior discontinuation of a topoisomerase I inhibitor due to treatment-relatedtoxicities.

• Have received an ADC consisting of a topoisomerase I inhibitor.

• Concurrent enrollment in another clinical study, unless it is an observationalclinical study.

• Inadequate washout period for prior anticancer treatment before the first dose ofstudy drug

• Undergone major surgery within 4 weeks before the first dose of study drug or expectmajor surgery during the study.

• Received long term systemic steroids or other immunosuppressive therapy within 2weeks before the first dose of study drug.

• Received any live vaccine within 4 weeks before the first dose of study drug orintend to receive a live vaccine during the study.

• Diagnosis or evidence of spinal cord compression or leptomeningeal carcinomatosis.

• Uncontrolled or clinically significant cardiovascular and cerebrovascular diseases.

• A history of non-infectious interstitial lung disease (ILD)/pneumonitis thatrequires steroids, current active ILD/pneumonitis.

• Have clinically severe pulmonary compromise resulting from intercurrent pulmonaryillnesses.

• Uncontrolled third-space fluid that requires repeated drainage.

• Digestive system disease that may cause bleeding, perforation, jaundice,gastrointestinal obstruction.

• An active tuberculosis based on medical history.

• Known human immunodeficiency virus (HIV) infection.

• Active hepatitis C infection.