Stage IIIB Non-small Cell Lung Cancer

This is a Phase II clinical trial evaluating the efficacy and safety of a new treatment approach for patients with locally advanced non-small cell lung cancer (NSCLC) that has spread to lymph nodes on the opposite side of the chest (known as N3 lymph node involvement). The study will enroll 28 patients aged 18 to 75 years with previously untreated, potentially resectable NSCLC classified as stage IIIB-IIIC. Participants will receive a combination of stereotactic body radiation therapy (SBRT) to the primary lung tumor, followed by two cycles of sintilimab (an immunotherapy drug) plus platinum-based chemotherapy before surgery. The main goals of the study are to see whether this treatment can shrink or eliminate cancer in the contralateral mediastinal lymph node (lymph node downstaging) and allow more patients to undergo curative surgery. Secondary goals include assessing pathological response rates, surgical outcomes, survival, and safety. Patients will be closely monitored during and after treatment, with follow-up visits planned for up to 5 years after surgery.

The goal of this observational study is to explore whether changes in peripheral blood effector tumor antigen-specific T cells (ETASTs) can predict treatment outcomes in patients with advanced non-small cell lung cancer (NSCLC) receiving chemoimmunotherapy. The study aims to: * Evaluate the relationship between ΔETAST levels (baseline to cycle 2) and progression-free survival * Compare the predictive performance of ΔETASTs with traditional biomarkers (PD-L1, TMB) * Assess whether ΔETASTs can identify patients more likely to benefit from PD-1 inhibitor plus chemotherapy Participants will: * Provide peripheral blood samples at baseline and after cycle 2 of treatment * Undergo ETAST quantification using the CTT-NanoDT technology with TATAN nanoparticles * Have standard tumor assessments every 2 cycles according to RECIST 1.1 criteria * Be followed for progression-free survival and overall survival up to 24 months

This is an observational study, aiming to investigate whether the ctDNA dynamics analyzed by the K-TrackTM assay could predict early response to Tyrosine kinase inhibitors (TKIs) in patients with advanced non-small cell lung cancer (NSCLC). 1. Determine relationship between ctDNA dynamics and clinical response to TKI, * No response/progressive disease = ctDNA levels increase from baseline * Partial response/stable disease = ctDNA levels decrease from baseline * Complete response = ctDNA clearance. 2. Compare and combine ctDNA dynamics and RECIST1.1 to predict clinical response. 3. Determine relationship between ctDNA dynamics and progression free survival, overall survival.