While associated with progression in colorectal, liver, pancreatic, and breast cancers through mechanisms like endothelial NF-κB/vascular endothelial growth factor A (VEGFA)-driven angiogenesis and periostin (POSTN)-mediated Integrin-linked protein kinase (ILK)/AKT/mTOR activation that fuels EMT and metastasis in hepatocellular carcinoma (HCC) (172–176), TMAO simultaneously enhances ICI response via context-dependent immunostimulation—with causality established through multiple experimental approaches. The gene discussed is POSTN; the disease is hepatocellular carcinoma.