Peripheral Blood ETASTs for Predicting Efficacy of Chemoimmunotherapy in NSCLC

Inclusion Criteria: * Histologically or cytologically confirmed stage IIIB-IV non-small cell lung cancer (NSCLC) * Planned to receive PD-1 inhibitor combined with platinum-based chemotherapy (e.g., pembrolizumab + pemetrexed/carboplatin) * Age 18-80 years * ECOG performance status 0-1 * Expected survival ≥12 weeks * Adequate bone marrow function: ANC ≥1.5×10⁹/L, PLT ≥100×10⁹/L * Adequate hepatorenal function: Cr ≤1.5×ULN, ALT/AST ≤2.5×ULN * At least one measurable lesion per RECIST 1.1 criteria * Able to provide informed consent and comply with study procedures including serial blood sampling and imaging follow-up Exclusion Criteria: * No measurable disease per RECIST 1.1 criteria * Tumor emergencies requiring immediate intervention (spinal cord compression, superior vena cava syndrome) * Active untreated central nervous system metastases or leptomeningeal disease * Prior treatment with immune checkpoint inhibitors within 4 weeks before enrollment * Chronic use of immunosuppressive agents (e.g., corticosteroids \>10 mg/day prednisone equivalent) * Coagulation disorders (INR \>1.5 or APTT \>1.5×ULN) or ongoing anticoagulation therapy * Poor vascular access precluding serial venipuncture (\>5 mL per draw) * Active hepatitis B (HBV DNA \>2000 IU/mL), hepatitis C, or HIV infection * Uncontrolled bacterial or fungal infection requiring systemic treatment * Pregnancy or lactation * Severe psychiatric disorder or communication barriers affecting informed consent or follow-up comp…