Plasma Protein Analysis for Biomarker Discovery in Lung Cancer Treated With Atezolizumab Combination Therapy in J‐ <scp>TAIL</scp> ‐2

J-TAIL-2 evaluated the efficacy and safety of atezolizumab, an anti-programmed death-ligand 1 (PD-L1), plus chemotherapy in patients with non-small cell lung cancer (NSCLC) and extensive-stage small cell lung cancer (ES-SCLC) in Japanese clinical practice, demonstrating comparable outcomes to those in the corresponding Phase 3 trials. Although PD-L1 expression is predictive of atezolizumab efficacy in some settings, additional minimally invasive, blood-based biomarkers are needed. This exploratory biomarker study included 359 J-TAIL-2 patients. The NSCLC cohort received atezolizumab combined with carboplatin and nab-paclitaxel (CnP, n = 42), cisplatin/carboplatin and pemetrexed (n = 72), or bevacizumab plus carboplatin and paclitaxel (bev + CP, n = 135). The ES-SCLC cohort received atezolizumab plus carboplatin and etoposide (n = 100). Approximately 560 cancer- or immune-related proteins were evaluated using the Proximity Extension Assay from blood plasma collected at three timepoints: baseline, before the second atezolizumab dose, and at the onset of immune-related adverse events (irAEs). Protein-wise comparisons were made to evaluate significant changes (P < 0.05 and > 0.5 log2 fold change) and linked to clinical outcomes reported in J-TAIL-2. IL-6, MUC-16, and KRT-19 were associated with shorter progression-free survival across multiple regimens. Granzyme A and B, immune activation markers, were elevated in responders who received atezolizumab + CnP and atezolizumab + bev + CP. High levels of baseline immune stimulation proteins were associated with irAEs across regimens. Protein expression changes were varied and regimen-dependent in subgroup analyses including older patients and those with EGFR-mutant tumors. These data warrant further investigation across different cancer types and atezolizumab-containing regimens to determine their relevance to efficacy and irAE occurrence of atezolizumab combination therapy. Trial Registration: ClinicalTrials.gov ID, NCT04501497 (J-TAIL-2) and NCT04818983 (biomarker study).