This is a multicenter, open-label study to evaluate the safety and tolerability of YL242 monotherapy and combination in participants with advanced solid malignant tumors.

Inclusion Criteria:

• Aged ≥18 years.
• Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 or 1
• Adequate organ and bone marrow function
• Tumor type:

Part 1-3: Advanced/unresectable or metastatic solid malignant tumor; Have received at least one prior line of systemic anti-tumor therapy

Part 4: locally advanced or metastatic non-sq NSCLC without AGA and HCC; Have not received any systemic anti-tumor therapy;

Part 5: mCRC, have received at least one (5a) or one (5b) prior line of systemic anti-tumor therapy

Part 6: advanced or metastatic HER2-negative G/GEJ; have received at least one (6a) or one (6b) prior line of systemic anti-tumor therapy

Exclusion Criteria:

• Be intolerant to prior treatment with a topoisomerase I inhibitor or an ADC that consists of a topoisomerase I inhibitor
• Uncontrolled or clinically significant cardiovascular and cerebrovascular diseases
• Clinically significant concomitant pulmonary disease
• A history of leptomeningeal carcinomatosis or carcinomatous meningitis
• Any illness, medical condition, organ system dysfunction, or social situation, including but not limited to mental illness or substance/alcohol abuse, deemed by the investigator to be likely to interfere with a patient's ability to sign informed consent, adversely affect the patient's ability to cooperate and participate in the study, or compromise the interpretation of study results