TLR4 and colorectal carcinoma: CRC is uniquely influenced by the gut microbiota: Fusobacterium nucleatum promotes MDSC/Treg enrichment via TLR4-NF-κB and Fap2-TIGIT pathways; Peptostreptococcus anaerobius acts through integrin-PI3K-NF-κB signaling; and microbial metabolites such as 4-HPA activate JAK2/STAT3-CXCL3 signaling to expand MDSC populations.