A Prospective, Single-Arm, Single-Center Phase II Study Evaluating the Efficacy and Safety of Chidamide Combined With PD-L1 Inhibitor, Carboplatin, and Etoposide as First-Line Treatment in Patients With Extensive-Stage Small-Cell Lung Cancer (ES-SCLC)

Inclusion criteria

• Age ≥18 and ≤75 years.
• Histologically confirmed ES-SCLC, unsuitable for local radical therapy.
• No prior systemic therapy for ES-SCLC.
• ECOG performance status 0-1.
• At least one measurable lesion per RECIST v1.1.
• Expected survival ≥3 months.
• Adequate organ function (hematological, hepatic, renal, cardiac).
• Effective contraception from consent until 180 days after last dose.
• For active HBV infection: HBV DNA \<2000 IU/mL within 28 days before treatment and on stable antiviral therapy.
• Recovery from prior therapy toxicities to ≤ Grade 1 (except alopecia).
• Signed informed consent.

Exclusion criteria

• Factors significantly affecting oral drug absorption.
• Prior HDAC inhibitor or immune checkpoint inhibitor therapy.
• Known allergy to any study drug component.
• Other malignancy within past 5 years (except certain cured cancers).
• Participation in another clinical trial within 4 weeks.
• Immunodeficiency, HIV positivity, or organ transplant history.
• Uncontrolled cardiovascular disease or QTc \>450 ms.
• Pregnancy, lactation, or unwillingness to use effective contraception.
• Other severe comorbid conditions deemed unsafe by investigator.
• History of neurological or psychiatric disorders.
• Any condition making the patient unsuitable per investigator judgment.