Abstract
ABSTRACT
Background
Tumor‐associated cell surface proteins are frequently proposed as circulating biomarkers for colorectal cancer (CRC) based on their high tumor expression. However, many candidates identified through tissue‐based analyses fail to translate into clinically useful biomarkers. We investigated the translational gap between tissue‐level expression and circulating detectability in CRC, focusing on molecular subtypes defined by caudal‐type homeobox 2 (CDX2) expression.
Methods
Transcriptomic data from The Cancer Genome Atlas (TCGA) were analyzed to identify cell surface markers differentially expressed between CDX2‐Low and CDX2‐High CRCs. A clinical cohort of right‐sided CRC patients was evaluated using paired tumor tissue and preoperative plasma samples. CDX2 expression was assessed by immunohistochemistry, and circulating concentrations of selected cell surface proteins were quantified using a multiplex ELISA platform.
Results
Several tumor‐associated cell surface markers exhibited marked CDX2‐dependent differences in tissue expression. However, for most markers, circulating plasma levels did not mirror tissue‐level patterns. CEACAM1 was the sole marker demonstrating concordant CDX2‐dependent differences in both tumor tissue and plasma, with significantly lower levels in CDX2‐Low CRCs. In contrast, CEACAM5 showed a dissociation between tissue expression and circulating levels, despite analytical validation against serum carcinoembryonic antigen (CEA).
Conclusions
Our findings demonstrate that tumor overexpression of cell surface markers does not necessarily translate into detectable circulating biomarkers. This translational disconnect underscores limitations of biomarker selection strategies based solely on tissue expression and highlights the importance of integrating systemic biology into biomarker development. While some tumor‐associated proteins may lack utility as circulating biomarkers, they may still represent viable therapeutic targets in CRC.