Beyond the barrier: Engineering the tumor-immune-soil nexus-a mechanistic blueprint for integrating Traditional Chinese Medicine with immunotherapy in metastatic colorectal cancer.

Metastatic colorectal cancer (mCRC) presents a stark immuno-oncologic dichotomy: while microsatellite instability-high (MSI-H) tumors respond to immune checkpoint inhibitors (ICIs), the vast majority of microsatellite-stable (MSS) cases remain refractory, underscoring a critical need for novel strategies to convert "cold" tumors into "hot" ones. This review advances the hypothesis that Traditional Chinese Medicine (TCM) can serve as a formula-defined ecological conditioner within the tumor-immune-soil nexus. We propose a mechanistic blueprint where TCM formulas, rather than acting as nonspecific immunostimulants, function as multi-target systems that re-engineer the tumor microenvironment. The framework integrates three actionable pillars: (1) remodeling the gut microbiome to restore immune-competent consortia and metabolic flux, (2) reprogramming the myeloid compartment away from suppressive M2 macrophages and MDSCs toward immunostimulatory states, and (3) inducing immunogenic cell death to generate critical danger signals. By translating classical concepts like the Gan Pi axis into modern immunometabolism, we propose that TCM can prime the "soil" to sensitize MSS mCRC to ICI therapy. However, realizing this potential requires a paradigm shift from descriptive reports to rigorous, biomarker-driven trials. A crucial point is that the nature of a significant portion of existing human evidence remains observational, cross-sectional, or case-control; this limits causal inference and hinders the reconstruction of the long-term temporal sequence extending from the reciprocal dynamics of the immune system and microbiome to cancer progression or treatment response. We conclude that the future of TCM-ICI integration lies in standardized, chemically characterized formulas evaluated within adaptive platform trials, utilizing spatial transcriptomics and microbiome-humanized models to validate true cold-to-hot conversion.