Integrative Profiling of Tumor and Blood Microenvironments to Uncover Molecular and Immune Determinants of Prognosis and Treatment Efficacy in Metastatic Colorectal Cancer

Metastatic colorectal cancer remains associated with poor prognosis despite major therapeutic advances, highlighting the need for robust biomarkers to refine treatment selection and monitor disease dynamics. This review summarizes emerging predictive and prognostic biomarkers in metastatic colorectal cancer across molecular and cellular layers, encompassing both tissue and circulating biomarkers. At the tissue level, we discuss genomic alterations and mutational signatures, transcriptomic classification systems and immune-related gene expression tools, protein-level immune checkpoint markers, and cellular determinants including immune infiltrates, cancer-associated fibroblasts and microbiome features. At the circulating level, we review biomarkers derived from liquid biopsy and peripheral blood, including circulating tumor DNA kinetics, T-cell receptor repertoire diversity, soluble cytokines and proteins, immune cell phenotyping, and circulating tumor cells. We highlight major challenges limiting clinical translation, including tumor heterogeneity, methodological variability, and the absence of standardized analytical pipelines and thresholds. Finally, we discuss future perspectives, emphasizing the integration of multi-omics biomarkers and artificial intelligence-driven strategies to improve biomarker validation and enable more precise management of metastatic colorectal cancer, particularly for patients with microsatellite-stable tumors who derive limited benefit from immune checkpoint inhibition.