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Introduction: Small-cell lung carcinoma (SCLC) is a high-grade neuroendocrine carcinoma of poor prognosis. Although immune checkpoint blockers have shown promising results in advanced SCLC, the tumor immune microenvironment (TME) remains poorly understood, with no validated prognostic or predictive biomarkers of efficacy., Methods: This retrospective study included surgically samples from 48 SCLC patients between 2009 and 2018. We assessed the TME using two quantitative 7-plex immunofluorescence panels focusing on T and B cells, and compared it to NSCLC (N = 10). Molecular subtypes were determined by assessing the expression of ASCL1, NEUROD1 and YAP1 using immunohistochemistry., Results: Immune-hot SCLC were defined as those exhibiting the highest immune cell and immune-related marker densities. They were associated with longer overall survival, significantly more frequently detected at early stages, and exhibited high PD-L1 expression in immune cells, but were not associated with molecular subtypes. Compared to NSCLC, SCLC had significantly lower densities of CD20 + cells and higher density of PD1 + cells, with no significant differences in CD4 + , CD8 + and plasma cell densities. In univariate analysis, the highest OS was significantly associated with early stage (p < 0.001), low expression of NEUROD1 (p = 0.047), high PD1 + cell density (p < 0.001) and high PD-L1 immune cell expression (p = 0.04). Only stage and PD1 + cell density emerged as independent prognostic markers., Conclusion: SCLC TME is highly heterogeneous. Immune-hot tumors were associated with OS but not with molecular classification. PD1 expression and PD-L1 expression by immune cells may thus serve as a prognostic marker., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Recent therapeutic advances in non-small cell lung cancer allow a better understanding of the interactions between the tumour and its direct immune environment. The identification of new immune biomarkers integrating both cell subpopulations and their interactions is a real issue in oncology. New techniques of tissue analysis, particularly multiplex immunohistochemistry, consisting of a labelling of several antigens of interest by immunofluorescence on the same slide, provide a better understanding of the tumour environment. Integration of these modalities of analysis to the therapeutic decision is promising, because it allows an increased characterization of each tumour, particularly interesting with radiotherapy and immunotherapy. This article describes the potential of these assays in locally advanced non-small cell lung cancer., (Copyright © 2018 Société française de radiothérapie oncologique (SFRO). Published by Elsevier Masson SAS. All rights reserved.)