Abstract 5298: Impact of targeted therapy on the tumor immune microenvironment in <i>EGFR</i>-mutated NSCLC

Abstract Background: In EGFR-mutated lung cancer, osimertinib, a third-generation EGFR tyrosine kinase inhibitor, has demonstrated durable efficacy in many cases. However, early resistance arises in some patients during treatment. The tumor immune microenvironment is believed to play a pivotal role in shaping treatment outcomes, though the detailed molecular mechanisms are not fully understood. Methods: This study analyzed four cases with paired tissue samples collected both before and after osimertinib treatment. Using Visium-HD, we performed analyses comparing the pre-treatment samples between the early resistance and long-term efficacy groups, as well as paired samples collected before and after treatment. We converted the Visium-HD spot data into single-cell data using StarDist, a deep learning-based method for nuclei/cell detection and segmentation. Furthermore, by adding the calculated coordinate data derived from StarDist to the single-cell data, we performed spatial transcriptome analysis using single-cell coordinates instead of spot coordinates. This enabled spatial transcriptomic analysis at the single-cell level while preserving the actual spatial relationships between cells. Results: In the post-treatment samples from early resistance cases, the proportion of macrophages, particularly SPP1-positive macrophages, was increased compared to that in long-term efficacy cases. In the comparison of pre-treatment samples between early resistance and long-term efficacy cases, the former exhibited a high degree of intermixing among diverse cell populations (e.g., lymphocytes, macrophages, and fibroblasts), whereas the latter showed minimal intermingling between tumor cells and other cell types. Furthermore, in early resistance cases, the expression levels of CXCR4 and CD74 were higher compared to long-term efficacy cases. Analysis of cell-cell interactions suggested potential effects of tumor cells on tertiary lymphoid structures. Conclusions: EGFR-mutated lung cancer is typically characterized by reduced immune cell infiltration, often referred to as “cold tumor.” However, early resistance cases exhibited increased immune cell infiltration and the presence of tertiary lymphoid structures, indicating a “hot tumor” phenotype. This finding suggests that EGFR-mutated lung cancer cases prone to early resistance might possess a tumor immune microenvironment resembling that of EGFR wild-type tumors. Citation Format: Daisuke Shibahara, Satoshi Nakamura, Yasuyuki kishikawa, Keita Nakatomi, Noriaki Nakagaki, Kohei Otsubo, Yoshimasa Shiraishi, Yasuto Yoneshima, Eiji Iwama, Kentaro Tanaka, Isamu Okamoto. Impact of targeted therapy on the tumor immune microenvironment in EGFR-mutated NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5298.