Characteristic <scp>miRNA</scp> profiles represent clinicopathological diversity of small cell lung cancer

Small cell lung cancer (SCLC) is classified into distinct molecular subtypes based on the expression patterns of four transcription regulators: achaete-scute homolog 1 (ASCL1), neuronal differentiation 1 (NEUROD1), POU class 2 homeobox 3 (POU2F3), and yes-associated protein 1 (YAP1). MicroRNAs (miRNAs) play critical roles in cancer cellular processes but their subtype-specific implications in SCLC remain underexplored. Out of 46 surgically resected SCLC samples, miRNA visualization through in situ hybridization identified high expression of miR-375 in the ASCL1, NEUROD1, and ASCL1/NEUROD1 subtypes, and miR-9-5p in the POU2F3 subtype. Comprehensive enhancer profiling using SCLC cell lines indicated that miR-375 and miR-9-5p were regulated by super-enhancers in a subtype-specific manner. Multiplex immunohistochemistry by imaging mass cytometry found that the miR-9-5p-high SCLC was characterized by a higher stromal area ratio, increased numbers of CD8⁺ T cells and CD163^- macrophages in the intra-tumoral area, and an increased number of plasma cells in the stromal area, as compared with the miR-9-5p-low SCLC. Finally, clinicopathological analysis revealed that the miR-375-high SCLC was associated with YAP1 downregulation, increased serum pro-gastrin-releasing peptide levels, and poor prognosis. These findings highlight the critical role of super-enhancer-related miRNAs in the diversity of SCLC, and underscore the potential for novel diagnostic and prognostic biomarkers based on these subtype-specific miRNAs. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.