Characteristic miRNA 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.