Inclusion Criteria:
1. Extensive-stage or locally advanced small cell lung cancer at initial diagnosis.
2. Confirmed by pathological histology/cytology combined with imaging.
3. ECOG PS 2-3 or age ≥65 years.
4. If a large number of comorbidities exist: ① mild failure or cachexia; ② mild bone marrow reserve dysfunction; ③ mild cardiovascular, liver, or kidney dysfunction, or dysfunction of other important organs; ④ mild infection, provided anti-infection treatment is administered; ⑤ mild water-electrolyte or acid-base imbalance, provided symptomatic treatment is given; ⑥ incomplete gastrointestinal obstruction caused by tumors; ⑦ other mild contraindications to anti-tumor therapy, if the investigator determines that the patient can be enrolled (reference: Modern Oncology, 3rd Edition, Tang Zhaoyou, Antitumor Drug Therapy, Contraindications), then patients with ECOG PS 0-1 and age \<65 are allowed.
5. Has measurable tumor target lesions (meeting RECIST 1.1 criteria).
6. Expected survival \> 3 months.
7. The functions of major organs meet the following requirements (excluding the use of any blood components and cell growth factors during the screening period):
1. Complete blood count (without blood transfusion or use of hematopoietic growth factors to correct the condition within 14 days): Hemoglobin (Hb) ≥90 g/L; Absolute neutrophil count (ANC) ≥1.5×10\^9 /L; Platelets (PLT) ≥100×10\^9 /L; White blood cell count (WBC) ≥3.0×10\^9 /L.
2. Biochemical tests: Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5×ULN (for patients with liver metastases, ≤ 5×ULN); serum total bilirubin (TBIL) ≤ 1.5×ULN (for subjects with Gilbert's syndrome, ≤ 3×ULN); serum creatinine (Cr) ≤ 1.5×ULN or creatinine clearance ≥ 50 ml/min.
3. Coagulation function: Activated partial thromboplastin time (APTT), international normalized ratio (INR), prothrombin time (PT) ≤1.5×ULN.
4. Doppler ultrasound assessment: Left ventricular ejection fraction (LVEF) ≥50%.
8. Women of childbearing age must have a negative pregnancy test (βHCG) before starting treatment. Women of childbearing age and men (who have sexual relations with women of childbearing age) must agree to use effective contraception continuously during the treatment and for 6 months after the last dose.
9. The patient voluntarily joined this study and signed the informed consent form.
Exclusion Criteria:
1. Within the past 2 years, having had or currently having other malignant tumors, except for cured basal cell carcinoma of the skin, carcinoma in situ of the cervix, superficial or non-invasive bladder cancer, etc.
2. Active tuberculosis infection.
3. Individuals with uncontrolled or symptomatic brain metastases, a history of poorly controlled psychiatric disorders, or severe intellectual or cognitive impairments.
4. Participants with active, known, or suspected autoimmune diseases, those with hypothyroidism requiring only hormonal replacement therapy, or those with skin conditions not requiring systemic treatment (such as vitiligo, psoriasis, or hair loss) can be included.
5. Pleural effusion, pericardial effusion, or ascites that cannot be controlled and require repeated drainage (patients whose effusion has been stable for 2 weeks or more after treatment can be enrolled).
6. Subjects with any of the following severe and/or uncontrolled diseases, including:
1. Subjects with poorly controlled blood pressure (systolic \>160 mmHg or diastolic \>100 mmHg).
2. Patients with ≥Grade 2 myocardial ischemia or myocardial infarction, severe arrhythmias (including QTc ≥450 ms in men, QTc ≥470 ms in women), and ≥Grade 2 congestive heart failure (New York Heart Association \[NYHA\] classification).
7. History of psychiatric medication abuse, alcoholism, or drug use.
8. Active hepatitis (for hepatitis B reference: HBsAg positive and HBV DNA test value greater than 500 IU/ml; for hepatitis C reference: HCV antibody positive and HCV viral load test value exceeding the upper limit of normal) human immunodeficiency virus (HIV, HIV 1/2 antibody) positive.
9. Severe bone marrow suppression is present.
10. Pregnant women or women who may be pregnant.
11. Patients who cannot comply with the trial protocol or cannot cooperate with follow-up.
12. Unable to swallow pills, malabsorption syndrome, or any condition that affects gastrointestinal absorption.
13. Researchers believe those who should not participate in this trial.
