A Study Comparing QLC5508 in Combination With QL2107 Versus Tislelizumab Plus Platinum-based Chemotherapy in Participants Wih Treatment-naïve Extensive-Stage Small Cell Lung Cancer

Inclusion criteria

• Age ≥18 years.
• Participants with histologically or cytologically confirmed Extensive-Stage Small Cell Lung Cancer (ES-SCLC) per the Veterans Administration Lung Cancer Study Group (VALG) staging system.
• No prior systemic treatment for ES-SCLC.
• At least one extracranial measurable lesion according to RECIST v1.1.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1, without deterioration within 2 weeks prior to the first dose of study treatment.
• Life expectancy ≥12 weeks.
• Has adequate organ function.
• Male and female participants of reproductive/childbearing potential must agree to avoid pregnancy.
• Voluntarily sign the written informed consent form and comply with the protocol requirements.

Exclusion criteria

• Has received or undergoing any of the following treatment:

Previous or current treatment with B7-H3 targeted therapy. Previous or current treatment with topoisomerase I inhibitors.

• Participants with transformed Non-Small Cell Lung Cancer (NSCLC), epidermal growth factor receptor (EGFR) mutation-positive NSCLC that has transformed to SCLC, or mixed SCLC-NSCLC histology.
• Presence with active brain metastases, leptomeningeal metastasis, brainstem metastasis or spinal cord compression.
• Radiotherapy with a limited field of radiation within 2 weeks prior to the study treatment; more than 30% of the bone marrow irradiation or large-scale radiotherapy within 4 weeks prior to study treatment.
• Major surgery within 4 weeks prior to the study treatment.
• Unresolved AEs ≥ Grade 2 (CTCAE v6.0) from prior therapy.
• Previous or concurrent primary malignancies.
• History of severe heart disease or cerebrovascular disease.
• History of Severe or uncontrolled hypertension or diabetes mellitus.
• Severe infection within 4 weeks prior to study treatment; or uncontrolled active infection at screening.
• Known or suspected interstitial lung disease/non-infectious pneumonitis; or other moderate to severe pulmonary diseases that significantly impair respiratory function and may interfere with the detection or management of drug-related pulmonary toxicity.
• Known history of pre-existing or newly diagnosed autoimmune disease.
• History of severe neuropathy or mental disorders.
• History of severe hypersensitivity reaction, severe infusion reaction or idiosyncrasy to drugs chemically related to study drugs or any components of the study drugs.
• Unlikely to comply with study procedures and requirements in the opinion of the investigator.
• Any disease or condition that, in the opinion of the investigator, would compromise participant safety or interfere with study assessments.