Accounting for 15–30% of colorectal cancer cases, the serrated pathway remains poorly characterized compared to the adenoma–carcinoma sequence. It involves sessile serrated lesions as precursors and is characterized by BRAF mutations (BRAF^V600E), CpG island hypermethylation, and microsatellite instability (MSI). Using label-free proteomics, we compared normal tissue margins from patients with diverticular disease, sessile serrated lesions, low-grade adenomas, and high-grade adenomas. We identified S100A14 as significantly overexpressed in sessile serrated lesions compared to low-grade adenomas, high-grade adenomas, and normal tissues. This overexpression was confirmed by immunohistochemical scoring in an independent cohort. Gene expression analyses of public datasets showed higher S100A14 expression in BRAF^V600E-mutated and MSI-H colorectal cancers compared to microsatellite stable BRAF^wt tumors. This finding was confirmed by immunohistochemical scoring in an independent colorectal cancer cohort. Furthermore, single-cell RNA sequencing analysis from the Human Colon Cancer Atlas revealed that S100A14 expression in tumor cells positively correlated with the abundance of tumoral CD8⁺ cytotoxic T cells, particularly the CD8⁺ CXCL13⁺ subset, known for its association with a favorable response to immunotherapy. Collectively, our results demonstrate for the first time that S100A14 is a potential biomarker of serrated neoplasia and further suggests its potential role in predicting immunotherapy responses in colorectal cancer.

Na⁺-K⁺-2Cl ⁻ cotransporter 1 (encoded by SLC12A2 ) is a solute carrier overexpressed in colorectal cancer (CRC), but its functional role remains unclear. Here, we identify NKCC1 as a marker of normal intestinal stem cells, supported by its crypt-base localization, single-cell transcriptomics, and patient-derived organoids, while analyses of public colorectal cancer single-cell datasets further link NKCC1 expression to cancer stem cell populations. Surprisingly, analysis of CRC patient datasets revealed that tumors with lower SLC12A2 expression were associated with poorer relapse-free survival. By stably knocking down NKCC1 in cell lines and organoids, we demonstrate enhanced expression of stemness markers, altered oxidative stress pathways, and increased radioresistance. In contrast, pharmacological inhibition with bumetanide activates AKT/mTORC1 signaling, elevates reactive oxygen species (ROS), and sensitizes cells to oxidative stress. Together, these results highlight NKCC1 as a dual regulator of stemness and redox homeostasis, supporting its role as a potential key player in colorectal carcinogenesis.