Longitudinal Whole-Exome Sequencing of Cell-Free DNA Reveals Molecular Evolution and Heterogeneous Clinical Outcomes in PD-L1 Stratified Advanced NSCLC Adenocarcinoma Patients Treated with Atezolizumab

Programmed death-ligand 1 (PD-L1) expression is routinely used to guide immune checkpoint inhibitor (ICI) therapy in advanced non-small cell lung cancer (NSCLC), yet clinical benefit remains heterogeneous even among PD-L1-high tumors. Liquid biopsy based on cell-free DNA (cfDNA) enables minimally invasive, real-time monitoring of tumor evolution. We report four cases of metastatic lung adenocarcinoma treated with atezolizumab, integrating longitudinal whole-exome sequencing (WES) of cfDNA with radiological assessment. Four patients with PD-L1-positive (≥60%) metastatic NSCLC received atezolizumab monotherapy. Serial cfDNA samples (1-3 per patient) were analyzed by high-depth WES. Distinct molecular trajectories paralleled divergent clinical outcomes. One patient achieved a complete molecular response, characterized by progressive clearance of KRAS, ATM, and NF1 mutant clones, which was concordant with radiological remission. A second patient showed an initial molecular response, followed by clonal rebound of TP53, NF1, and NOTCH2 mutant populations and the emergence of PTEN and KIF1A variants, suggesting clinical progression. Two patients exhibited primary resistance despite high PD-L1 expression, with persistent or expanding clones and early subclonal diversification; in one case, new EGFR and BRAF alterations emerged under treatment pressure. Notably, switching to platinum-based chemotherapy in a non-responder induced a measurable molecular response, highlighting discordance between PD-L1 status and immunotherapy efficacy. Longitudinal cfDNA WES captured dynamic clonal remodeling under immunotherapy and anticipated radiological outcomes. These findings underscore the clinical necessity of integrating dynamic molecular monitoring by liquid biopsy to overcome the limitations of static PD-L1 assessment, refine therapeutic stratification, and identify early resistance mechanisms in advanced NSCLC.