Biomarker exploration for immunotherapy plus chemotherapy following resistance to third-generation EGFR-TKIs in lung adenocarcinoma.

BACKGROUND: The efficacy of immune checkpoint inhibitor plus chemotherapy (ICI-chemo) following third-generation EGFR-TKI resistance in EGFR-mutant lung adenocarcinoma (LUAD) is variable and lacks reliable predictive biomarkers. This study investigated associations between treatment-naïve primary tumor transcriptomic profiles, tumor immune microenvironment (TIME) characteristics, and subsequent ICI-chemo efficacy. METHODS: This retrospective study enrolled 12 advanced LUAD patients who received ICI-chemo after progressing on third-generation EGFR-TKIs. Patients were stratified into Better (N = 7) and Worse (N = 5) efficacy groups using 6-month progression-free survival (PFS) as cutoff. Treatment-naïve tumor specimens were analyzed using Digital Spatial Profiling (DSP) whole transcriptome sequencing and multiplex immunofluorescence (mIF) to assess compartment-specific gene expression, pathway enrichment, and infiltration of 19 immune cell types. LASSO-Cox regression was performed to identify key prognostic genes. RESULTS: SFTPC expression was significantly elevated across all compartments in the Worse efficacy group. Enrichment analysis revealed that the efficacy of ICI-chemo in EGFR-mutant patients arises from a combination of proliferative tumor cells and an activated TIME. A total of eight key prognostic genes were identified: DNM1L_Immune, ADPGK_Immune, SLC12A4_Stroma, PLA2G6_Immune, FKBP1A_Immune, CHST15_Tumor, TRMT5_Immune, TAX1BP1_Immune. Complex correlations were observed between these key genes and the expression of immune checkpoints. mIF revealed significantly higher infiltration of cancer-associated fibroblast subtype I (CAFI) in the Worse group, while the Better efficacy group exhibited a more activated antitumor TIME. CONCLUSIONS: Baseline upregulation of SFTPC, enrichment of CAFI, and specific immune checkpoint expression patterns are associated with poor response to ICI-chemo following EGFR-TKI resistance in EGFR-mutant LUAD. The eight spatially resolved genes identified may serve as potential predictive biomarkers for patient stratification. These findings underscore the functional interdependence between tumor-intrinsic properties and TIME characteristics in determining immunotherapy outcomes, and provide biologically plausible candidates warranting independent validation in larger cohorts.