S100A14 as a Potential Biomarker of the Colorectal Serrated Neoplasia Pathway.

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.