PURPOSE: DNA damage response and repair (DDR) gene alterations contribute to genomic instability and increased tumor immunogenicity, yet their clinical significance in non-small cell lung cancer (NSCLC) remains unclear. Using a large real-world dataset, we evaluated the prevalence of DDR alterations and their relation to the tumor immune microenvironment in metastatic NSCLC. EXPERIMENTAL DESIGN: We retrospectively analyzed real-world data from patients with metastatic NSCLC using the Tempus AI database. Tumors were sequenced with Tempus xT DNA and xR RNA assays and classified based on the presence (DDRmt) or absence (DDRwt) of a pathogenic somatic alteration or copy number deletion in a DDR pathway gene. Associations between DDR alterations and immune cell infiltration, PD-L1 immunohistochemistry, tumor mutational burden (TMB), and microsatellite instability (MSI-H) were examined. RESULTS: Among 14,127 patients (median age = 67, 49% female), 5,276 (37%) were DDRmt. There was a higher prevalence of current/former smokers in the DDRmt group (86% vs. 82%
p<
0.001). DDRmt tumors were more likely to have higher levels of TMB (median: 5.4 vs. 4.6
p<
0.001), MSI-H (1.1 % vs. <
0.1 %
p<
0.001), and infiltrating CD8 CONCLUSIONS: Among patients with metastatic NSCLC, 37% present with DDRmt tumors characterized by higher TMB, frequency of MSI-H, and changes in immune cell infiltrates. These findings provide insight into the immunogenic landscape of DDR-altered NSCLC and may inform biomarker selection and therapeutic strategies.