Abstract Background: Immune checkpoint inhibitors (ICIs) improve survival in advanced non-small cell lung cancer (NSCLC), but their benefits are limited in EGFR-mutant NSCLC. ICIs are often used after resistance to EGFR tyrosine kinase inhibitors (EGFR-TKIs). Since EGFR-TKI treatment alters the tumor microenvironment, predictive biomarkers for ICI response should ideally be identified post-EGFR-TKI resistance. However, obtaining re-biopsy samples is challenging. This study explores predictive biomarkers for ICI response using plasma samples collected before and after EGFR-TKI therapy. Methods: We retrospectively analyzed 28 EGFR-mutant NSCLC patients treated with ICIs at Inha University Hospital (2016-2023). All patients received first-line EGFR-TKI therapy and transitioned to ICIs after resistance. Plasma samples were collected before EGFR-TKI initiation and post-resistance. Ninety-six plasma proteins were quantified using the Olink Immuno-Oncology panel. PD-L1 expression in tumor tissues was assessed at diagnosis with SP263 or 22C3 assays. Progression-free survival (PFS) was defined as time from ICI initiation to progression. Responders were defined as PFS ≥6 months, and non-responders as PFS <6 months. Results: Among 28 patients, 25 had adenocarcinoma, 1 squamous cell carcinoma, 1 adenosquamous carcinoma, and 1 poorly differentiated NSCLC. EGFR mutations included exon 19 deletion (n=14), L858R (n=10), and uncommon mutations (n=4). First-line EGFR-TKIs included erlotinib (n=15), afatinib (n=9), and gefitinib (n=4). T790M mutations were identified in 11 patients, of whom 10 received osimertinib and 1 received lazertinib. ICIs included atezolizumab (n=15), pembrolizumab (n=5), and nivolumab (n=8). PD-L1 expression was evaluated in 23 patients using SP263 (5 negative, 15 with 1-49%, 3 with ≥50%) and in 22 patients using 22C3 (7 negative, 11 with 1-49%, 4 with ≥50%). Median PFS for ICIs was 2.7 months (95% CI: 1.7-3.7), with 6 responders and 22 non-responders. Plasma levels of IL-4, IL-6, GZMH, and Gal-9 differed significantly between responders and non-responders post-EGFR-TKI resistance. These findings were validated using tissue samples obtained post-resistance. Progression-free survival (PFS) showed significant differences according to plasma biomarker expression. Conclusions: Plasma samples collected after EGFR-TKI resistance can predict ICI responses in EGFR-mutant NSCLC. Post-resistance plasma biomarker levels may serve as a minimally invasive approach to guide therapeutic decisions in this challenging patient population. Citation Format: Jun Hyeok Lim, Min Seok Park, Nuri Park, Yejin Cho, Sehan Kwak, Beom Seok Han, Minseo Lee, Donghyun Seo, Woo Kyung Ryu, Jeong-Seon Ryu, Soon-sun Hong, Kyung Hee Jung. Blood-based biomarkers for predicting treatment response to immune checkpoint inhibitors after EGFR-TKI resistance [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 4617.

Abstract Cancer senescence induced by conventional chemotherapy and radiotherapy, characterized by limited proliferation, drug resistance, and a senescence-associated secretory phenotype, is increasingly recognized as a contributor to cancer relapse and the development of an immunosuppressive tumor microenvironment. However, the relationship between cancer senescence and anti-tumor immunity remains poorly understood. In this study, we demonstrate that senescent cancer cells upregulate PD-L1 expression by enhancing its transcription and glycosylation. We identify ribophorin 1 as a key regulator of PD-L1 glycosylation during cancer senescence. Ribophorin 1 depletion significantly reduces PD-L1 levels through the ER-lysosome-associated degradation pathway, rendering senescent cancer cells more susceptible to T-cell-mediated killing. Furthermore, ribophorin 1 depletion suppresses tumor growth by decreasing PD-L1 levels and enhancing cytotoxic T lymphocyte (CTL) activity. Additionally, targeting ribophorin 1 or using anti-PD-1 therapy effectively reduces the number of senescent cancer cells in irradiated tumors and suppresses cancer recurrence by activating CTLs. These findings clarify how senescent cancer cells evade T-cell immunity following treatment, contributing to cancer recurrence. Our results highlight the therapeutic potential of targeting senescent cancer cells as a strategy in cancer treatment. Citation Format: Hyun Jung Hwang, Donghee Kang, Jisoo Shin, Jonghun Jung, Soyeon Ko, Kyung Hee Jung, Soon-Sun Hong, Ji Eun Park, Myung Jin Oh, Hyun Joo An, Wen-Hao Yang, Young-Gyu Ko, Minji Choi, Jong-Ho Cha, Jae-Seon Lee. Therapy-induced senescent cancer cells facilitate immune evasion in cancer by promoting PD-L1 upregulation through a ribophorin 1-dependent pathway [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 2556.