An L1CAM-Positive Fibroblast-Associated Stromal State Is Associated with Reduced T/NK Cytotoxicity Features in...

Background/Objectives: L1 cell adhesion molecule (L1CAM) has been implicated in colorectal cancer progression, but its cellular source and immune microenvironmental context remain incompletely defined. This study aimed to characterize the expression pattern, cellular localization and immune-associated features of L1CAM in colorectal cancer using public bulk and single-cell datasets. Methods: TCGA, GTEx and CPTAC/UALCAN datasets were used to assess L1CAM expression, protein abundance and clinical associations across cancers, with a focus on colorectal cancer. Single-cell RNA sequencing data from GSE178341 were analyzed to identify L1CAM-expressing cell populations, characterize transcriptional programs and evaluate sample-level associations with immune-cell composition and T/NK cytotoxicity signatures. Candidate ligand-receptor interactions and conceptual mod el-based sensitivity analyses were used to explore stromal-immune communication axes. Supplementary external single-cell datasets were analyzed exploratorily. Results: In colorectal cancer, L1CAM showed tumor-normal expression differences and was associated with progression-free interval, but not overall survival. Single-cell analysis detected L1CAM mainly in rare fibroblast and epithelial subsets rather than T/NK cells. L1CAM-positive fibroblasts showed neural-like, wound-response and matrix-remodeling transcriptional features. In the main cohort, L1CAM-Fib+ samples showed lower T/NK cytotoxicity transcriptional signatures, whereas supplementary external datasets did not reproduce the same direction of association. Candidate communication analyses nominated Galectin, HLA-E, TGFB and extracellular matrix-related axes. Conclusions: These findings suggest that L1CAM-positive fibroblast-associated stromal states provide a dataset-specific exploratory context for interpreting L1CAM-associated immune features in colorectal cancer. The results should be considered hypothesis-generating and require spatial and functional validation.