Assessment of Adebelizumab Combined with Chemotherapy in Concurrent Radiotherapy Versus Sequential Radiotherapy As First-Line Treatment for Extensive-Stage Small Cell Lung Cancer

Inclusion Criteria:

• Age ≥18 years, no gender restrictions;

• Confirmed pathological diagnosis of extensive-stage small cell lung cancer (ES-SCLC), defined as disease extending beyond one hemithorax, including malignantpleural and pericardial effusions or hematogenous metastases (according to theVeterans Administration Lung Cancer Study Group, VALG staging); stage IV (any T, anyN, M1a/b/c) according to the AJCC (8th edition), or T3-4 due to multiple pulmonarynodules or tumor/nodule size too large to be included in a tolerable radiationtherapy plan;

• Participants have not received systemic treatment for extensive-stage SCLC;

• No more than 5 lesions (including metastatic foci), with at least one measurablelesion (according to RECIST v1.1);

• ECOG performance status score of 0-2;

• Life expectancy ≥3 months;

• Consented and signed the informed consent form, willing and able to comply withplanned visits, study treatments, laboratory tests, and other trial procedures;

• Normal major organ function, meeting the following criteria (without symptomatictreatment within 14 days): a) Hematology:

Hemoglobin (Hb) ≥90g/L; Platelet (PLT) ≥100×10^9/L; Neutrophil count (ANC) ≥1.5×10^9/L; White blood cell count (WBC) ≥3.0×10^9/L;

Lymphocyte ≥0.5×10^9/L; b) Biochemistry:

Alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) ≤ 2.5×ULN; For those with liver metastasis, ALT, AST≤5 ULN; For those with liver or bone metastasis: ALP ≤5 ULN; Total serum bilirubin (TBIL) ≤1.5×ULN (for Gilbert's syndrome participants ≤3×ULN); Albumin (ALB) ≥3 g/dL;

Renal function: Serum creatinine ≤1.5 x ULN or creatinine clearance rate (CrCl) ≥50mL/minute (using Cockcroft/Gault formula); c) Coagulation:

Activated partial thromboplastin time (APTT), International Normalized Ratio (INR), Prothrombin Time (PT) ≤1.5×ULN; d) Others: Lipase ≤1.5 x ULN. Participants with lipase >1.5 x ULN without clinical or radiological evidence of pancreatitis can be included; e) Doppler echocardiography: Left ventricular ejection fraction (LVEF) ≥50%;

• Female participants of childbearing potential must have a negative serum HCG testwithin 72 hours before the first dose, not breastfeeding, and must use a medicallyrecognized contraceptive method (such as intrauterine devices, birth control pills,or condoms) during the study treatment and for 2 months after the last dose ofAdebrelimab or 6 months after the last dose of Carboplatin/Etoposide (whichever islonger); male participants with partners of childbearing potential must besurgically sterilized or agree to use highly effective contraception during thetrial and for 2 months after the last dose of Adebrelimab or 3 months after the lastdose of Carboplatin/Etoposide (whichever is longer), and no sperm donation duringthe study.

Exclusion Criteria:

• Participants who have previously received any T-cell co-stimulation or immunecheckpoint therapy, including but not limited to cytotoxic T-lymphocyte-associatedantigen-4 (CTLA-4) inhibitors, PD-1 inhibitors, PD-L1/2 inhibitors, CD137 agonists,or other T-cell targeted drugs.

• Participants who have previously received chemoradiotherapy for limited-stage SCLC;

• Participants with clinically symptomatic central nervous system metastases (such asbrain, spinal cord), or leptomeningeal metastases; participants with active or newCNS metastases found on imaging during the screening period are not included. (Asymptomatic untreated CNS metastases with a lesion size <1cm are allowed to beincluded);

• Participants with multiple liver metastases (isolated liver metastasis participantswith metastasis <2cm can be included)

• Participants with spinal cord compression;

• Participants with active autoimmune diseases requiring systemic treatment (such asdisease-modifying drugs, corticosteroids, or immunosuppressants) within 2 yearsbefore the first dose, or with a history of autoimmune diseases and expectedrecurrence. Replacement therapies (such as thyroid hormone, insulin, orphysiological corticosteroids for adrenal or pituitary insufficiency) are notconsidered systemic treatment;

• Diagnosed with immune deficiency or receiving systemic glucocorticoid treatment orany other form of immunosuppressive therapy within 14 days before the first dose;the use of physiological doses of glucocorticoids (≤10 mg/day of prednisone orequivalent) is allowed;

• Participants who have had arterial/venous thrombotic events within 6 months beforethe first dose, such as cerebrovascular accidents (including transient ischemicattacks, cerebral hemorrhage, cerebral embolism, etc.), deep vein thrombosis, andpulmonary embolism;

• Participants with a history of idiopathic pulmonary fibrosis, organizing pneumonia (such as cryptogenic organizing pneumonia), drug-induced pneumonia, or idiopathicpneumonia, or evidence of active pneumonia on chest computed tomography (CT) atscreening (participants with active tuberculosis are not included);

• Participants who have undergone major surgical treatment or significant traumaticinjury within 28 days before the first dose;

• Participants who have received or plan to receive preventive vaccines orlive-attenuated vaccines within 4 weeks before the first dose;

• Participants who have received other trial medications or participated in anotherinterventional clinical study within 4 weeks before signing the ICF;

• Participants with other malignancies that require active treatment within 5 years (except for those with a >90% 5-year survival rate such as fully treated basal cellor squamous cell skin cancer, cervical carcinoma in situ, localized prostate cancerafter radical surgery, localized bladder cancer, ductal carcinoma in situ afterradical surgery, or in situ breast cancer);

• Participants with any severe and/or uncontrolled diseases, including: a)Uncontrolled hypertension (systolic blood pressure ≥140 mmHg or diastolic bloodpressure ≥90mmHg) participants; history of hypertensive crisis or hypertensiveencephalopathy; b) Uncontrolled cardiac clinical symptoms or diseases such as ≥grade 2 myocardial ischemia or myocardial infarction, uncontrollable arrhythmias (including men QTc ≥450ms, women QTc ≥470ms), and ≥grade 2 congestive heart failure (New York Heart Association, NYHA classification), unstable angina, myocardialinfarction within 24 weeks, clinically significant supraventricular or ventriculararrhythmias requiring treatment or intervention; c) Active or uncontrolled severeinfections (≥CTC AE grade 2 infections), including but not limited tohospitalization due to infectious complications, bacteremia, or severe pneumonia,unexplained fever >38.5℃ before the first dose. d) Liver cirrhosis, activehepatitis*; *Active hepatitis - Hepatitis B reference: HBsAg positive, exceeding theupper limit of normal (1000 copies/ml or 500 IU/ml); participants with pastHepatitis B virus (HBV) infection or cured HBV infection (defined as the presence ofhepatitis B core antibody [HBcAb] and absence of HbsAg, and normal HBV DNA valuesdetected during the screening period can be included; *Hepatitis C reference: HCVantibody positive, and HCV viral load exceeds the upper limit of normal/HCV RNA orHCV Ab indicates acute or chronic infection; e) HIV positive or known AcquiredImmune Deficiency Syndrome (AIDS); f) Urine routine suggests urinary protein ≥++,and confirmed 24-hour urinary protein quantification >1.0 g;

• Participants with clinically symptomatic third-space fluid accumulation, such aspericardial effusion, pleural effusion, and abdominal effusion requiring repeateddrainage (such as once a month or more frequently) that cannot be controlled bytapping or other treatments;

• Participants whose adverse events (except for alopecia) caused by previoustreatments have not recovered to ≤CTCAE grade 1; other toxicities caused by previousantitumor treatments that are expected to be unresolved and have long-termpersistent sequelae, such as neurotoxicity caused by platinum-based treatments, areallowed to be included;

• Known history of allogeneic organ transplantation or allogeneic hematopoietic stemcell transplantation;

• Known history of drug abuse that cannot be quit, mental disorders, alcoholism, drugabuse, or substance abuse;

• Known allergy to study drugs or excipients, known severe allergic reactions to anymonoclonal antibody;

• As judged by the investigator, there are factors that seriously endanger the safetyof the participants or other factors that may lead to the forced termination.