Abstract Background: Immunotherapy is firmly established as a treatment regimen in various solid tumors due to its exceptional benefits observed in a select group of patients. Despite widespread use of immune checkpoint blockade (ICB) across diverse solid tumors, including non-small cell lung cancer (NSCLC), the quest for a clinically informative biomarker for long-term benefit remains unmet. Here we investigate the potential utility of clinicopathological and spatial proteomic profiling of tumor specimens from NSCLC patients to identify predictive biomarkers of long-term benefit to ICB. Methods: Forty-nine patients diagnosed with advanced NSCLC who received ICB at Hospital del Mar, Barcelona between 2017-2021 were included. Long-term responders (LTR, n=21) were defined as patients achieving a maintained radiologic response for more than 2 years, and short-term responders (STR, n=28) as patients presenting disease progression within the first six months of ICB initiation. Clinicopathological information, incidence of immune related adverse (irAES) and PD-L1 tumor proportion score assessed by IHC was available for all of them. DSP GeoMx was performed in subset of patients (LTR n=14 and STR n=14), to assess 49 immune biomarkers. Pancytokeratin (panCK; epithelial), CD3, CD20 and SYTO 13 (nuclear) were utilized as morphology biomarkers. Regions of interest were placed in tissue areas containing tumor and segmented in Tumor (PanCK+) and tumor microenvironment (TME) (PanCK-) that was used on downstream analysis. Digital counts were normalized using the protein expression of housekeeper proteins. Statistical analysis was performed using linear mixed models. A P value less than 0.05 was considered significant. Results: Our analysis revealed specific characteristics of LTR patients compared with STR, namely LTR population was enriched for PD-L1 positive in tumors (p=0.005) and a higher incidence of immune-related adverse events (irAEs) (p=0.001). Within the Tumor compartment, LTR patients displayed significantly higher levels of IDO1, CD8, PD-L1, CD45, HLA-DR and STING, while STR patients exhibit higher levels of B7-H3, CD56 and OX40L (p<0.05 for all proteins). Comparison analysis of the TME compartment between LTR and STR revealed augmented levels of IDO1, CD8, CD45, CD11c, CD27 and CD3 in LTR patients, and lower levels of B7H3 and OX40L compared with STR patients (p<0.05 for all proteins). Conclusions: Our comprehensive analysis of metastatic NSCLC patients treated with ICB has unveiled distinct clinicopathological and immunological features associated with long-term benefit of ICB, highlighting the presence of pre-existing antitumor immunity as a stronger predictor of long-term benefit. These findings offer insights into potential biomarkers and therapeutic strategies for enhancing ICB outcomes in metastatic NSCLC. Citation Format: Sharia Hernandez, Rafael Bach, Mario Giner, Wei Lu, Larisa Kostousov, Sean Barnes, Khaja Khan, Laura Masfarré, Xavier Villanueva, Ignacio Sanchéz, Nil Navarro, Álvaro Taus, Miguel Galindo, Max Hardy, Raúl Del Rey-Vergara, Albert Iñañez, Beatriz Sanchez-Espiridion, Laura Moliner, Sergi Clavé, Beatriz Bellosillo, Ana Rovira, Júlia Perera-Bel, Ignacio Wistuba, Edurne Arriola, Luisa M. Solis, Pedro Rocha. Spatial proteomic profiling unveils pre-existing anti-tumor immunity as a hallmark of exceptional benefit from immunotherapy in NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6391.

Introduction: Neoadjuvant and adjuvant immune checkpoint blockade (ICB) have recently become standard of care in resectable non-small cell lung cancer (NSCLC). Yet, biomarkers that inform patients who benefit from this approach remain largely unknown. Here, we interrogated the tumor immune microenvironment (TIME) in earlystage NSCLC patients that underwent up-front surgery. Methods: A total of 185 treatment-naive patients with early-stage NSCLC, that underwent up-front surgical treatment between 2006 and 2018 at Hospital del Mar were included. 124 lung adenocarcinomas (LUADs), and 61 squamous cell carcinoma (LUSCs) were included in a tissue microarray. Immunohistochemistry for CD3, CD4, CD8, CD68, CD80, CD103, FOXP3, PD-1, PD-L1, PD-L2 and HLA class II were evaluated by digital image analysis (QuPath software). TIME was categorized into four groups using PD-L1 expression in tumor cells (<1 % or & GE;1 %) and tumor resident memory (CD103+) immune cells (using the median as cut-off). We explored the association between different TIME dimensions and patient's clinicopathological features and outcomes.Results: We found increased levels of T cell markers (CD3+, CD4+, CD8+ cells), functional immune markers (FOXP3+ cells) as well as, higher HLA-II tumor membrane expression in LUADs compared to LUSCs (p < 0.05 for all). In contrast, LUSCs displayed higher percentage of intratumor macrophages (CD68+ cells) as well as, higher PD-L1 and PD-L2 tumor membrane expression (p < 0.05 for all). Unsupervised analysis revealed three different tumor subsets characterized by membrane tumor expression of PD-L1, PD-L2 and HLA-class II. Enrichment of T cells (CD3+, CD8+ cells), regulatory T cells (FOXP3+ cells) and macrophages (CD68+ cells) was observed in the CD103+/PD-L1+ group (p < 0.05 for all). Multivariate analysis showed that infiltration by CD103+ immune cells was associated with improved OS (p = 0.009).Conclusions: TIME analysis in resected NSCLC highlighted differences by histology, PD-L1 expression and molecular subgroups. Biomarker studies using IHC might aid to individually tailor adjuvant treatment in early-stage NSCLC.