Characterization of tumor‐associated macrophages and the immune microenvironment in limited‐stage neuroendocrine‐high and ‐low small cell lung cancer

This study aims to characterize tumor‐infiltrating macrophages (TAMs), myeloid‐derived suppressor cells (MDSC), and the related molecular milieu regulating anti‐tumor immunity in limited‐stage neuroendocrine (NE)‐high and NE‐low small cell lung cancer. Primary tumors and matched lymph node (LN) metastases of 32 resected, early‐stage SCLC patients were analyzed by immunohistochemistry (IHC) with antibodies against pan‐macrophage marker CD68, M2‐macro-phage marker CD163, and MDSC marker CD33. Area‐adjusted cell counting on TMAs showed that TAMs are the most abundant cell type in the TME, and their number in tumor nests exceeds the number of CD3 + T‐cells (64% vs. 38% in NE‐low and 71% vs. 18% in NE‐high). Furthermore, the ratio of CD163‐expressing M2‐polarized TAMs in tumor nests was significantly higher in NE‐low vs. NE‐high tumors (70% vs. 31%). TAM density shows a strong positive correlation with CD45 and CD3 in tumor nests, but not in the stroma. fGSEA analysis on a targeted RNAseq oncological panel of 2560 genes showed that NE‐high tumors exhibited increased enrichment in pathways related to cell proliferation, whereas in NE‐low tumors, immune response pathways were significantly upregulated. Interestingly, we identified a subset of NE‐high tumors representing an immune‐oasis phenotype, but with a different gene expression profile compared to NE‐low tumors. In contrast, we found that a limited subgroup of NE‐low tumors is immune‐deserted and express distinct cellular pathways from NE‐high tumors. Furthermore, we identified potential molecular targets based on our expression data in NE‐low and immune‐oasis tumor subsets, including CD70, ANXA1, ITGB6, TP63, IFI27, YBX3 and CXCR2.