The concept of the pre-metastatic niche dates back to Stephen Paget’s 1889 seed and soil hypothesis, which proposed that metastasis depends on compatible interactions between cancer cells and the organ-specific microenvironment they colonize. Modern research has refined this idea considerably. Primary tumors release soluble factors such as TGF-β and VEGF, along with extracellular vesicles carrying molecular cargo, that travel through the bloodstream and condition distant organs. Bone marrow-derived cells are recruited to these sites, local stroma is remodeled, and vasculature is altered. The result is a patch of tissue that is inflamed, immunosuppressed, and metabolically reprogrammed — fertile ground for any tumor cell that arrives. The liver, because of its unique anatomy and immunological profile, is particularly susceptible to this kind of preparation.

What makes the liver special is its blood supply. Approximately 75 percent of hepatic blood arrives via the portal vein, which drains directly from the intestines. This means the liver is continuously bathed in gut-derived nutrients, microbial products, and metabolites. Under normal conditions, this arrangement sustains immune tolerance and metabolic homeostasis. But in tumor-bearing hosts, the gut microbiota undergoes profound compositional shifts, and the signals traveling through the portal vein transition from physiological to pathological. The review identifies this transition as the primary instigator of hepatic pre-metastatic niche formation.

The evidence for tumor-associated gut dysbiosis is now extensive across multiple cancer types. In colorectal cancer, a landmark multi-omics analysis by Yachida and colleagues of 616 individuals undergoing colonoscopy demonstrated that microbial and metabolomic shifts are detectable even at the stage of multiple polypoid adenomas and intramucosal carcinomas. Fusobacterium nucleatum was continuously elevated from intramucosal carcinoma through more advanced stages, while Atopobium parvulum and Actinomyces odontolyticus were enriched specifically in early lesions. Metabolomically, branched-chain amino acids and phenylalanine were elevated in intramucosal carcinoma, and bile acids including deoxycholate accumulated in adenomas. A meta-analysis by Wirbel and colleagues across eight geographically distinct cohorts confirmed consistent enrichment of Fusobacterium nucleatum and Porphyromonas asaccharolytica alongside depletion of butyrate-producing taxa such as Roseburia and Eubacterium. Critically, these dysbiotic profiles differ between non-metastatic and metastatic disease, with metastatic patients showing enrichment of Pyramidobacter, Christensenellaceae_R-7_group, and Romboutsia.

The pattern extends well beyond colorectal cancer. In breast cancer, shotgun metagenomic sequencing of fecal samples from 38 patients and 36 matched controls revealed depletion of beneficial taxa including Limosilactobacillus fermentum and Blautia species, enrichment of Prevotella copri, and reduced short-chain fatty acid and purine metabolism pathways. A machine learning model integrating microbial and metabolic features achieved an area under the curve of 0.78 in the discovery cohort and 0.73 in an independent validation cohort. In non-small cell lung cancer, compositional shifts were pronounced across TNM stages, with Bacteroides predominating in stage T2, Prevotella in stage T4, and Ruminococcus gnavus elevated in stages N3 and M. Gastric cancer displays progressive dysbiosis with pathogenic Fusobacteria and Bacteroides caccae increasing with disease progression while Bifidobacterium longum is depleted. In pancreatic ductal adenocarcinoma, a fecal microbiota signature with high specificity has been defined across multi-center cohorts, and the microbiota-derived tryptophan metabolite indole-3-acetic acid has been shown to influence chemotherapy response through neutrophil myeloperoxidase-dependent reactive oxygen species metabolism.

Once these dysbiotic signals reach the liver, they are sensed and amplified by a complex cellular network. Hepatocytes, which constitute 60 percent of hepatic cells and 80 percent of total liver volume, are the first parenchymal cells exposed to gut-derived factors via the portal vein. Research has shown that fatty liver upregulates hepatocyte Rab27a, promoting secretion of extracellular vesicles enriched with specific microRNAs that suppress LATS2 in colorectal cancer cells, activating YAP-CYR61 signaling and promoting M2-like macrophage infiltration alongside CD8-positive T-cell exhaustion. Colorectal cancer-derived small extracellular vesicles can also induce TGFβ1-mediated epithelial-mesenchymal transition in hepatocytes, generating a pro-fibrotic and pro-tumorigenic hepatic milieu. Loss of hepatocyte metabolic defense, through knockout of prohibitin 1 or methionine adenosyltransferase α1, markedly increases hepatic metastasis in experimental models.

Liver sinusoidal endothelial cells, which comprise approximately 50 percent of liver non-parenchymal cells, serve as the first barrier to gut-derived molecules and circulating tumor cells. During pre-metastatic niche formation, tumor-derived factors and inflammation upregulate adhesion molecules including ICAM-1, promoting tumor cell arrest and transmigration. Blocking ICAM-1 reduced liver tumor retention by 50 percent and metastatic burden by 75 percent in experimental models. Cancer-derived extracellular vesicles carrying AMIGO2 further enhance tumor-endothelial adhesion. Metabolic liver disease and inflammation induce LSEC defenestration and capillarization, and steatohepatitis-associated vascular remodeling has been shown to promote melanoma liver metastasis, indicating that pre-existing endothelial dysfunction creates a pro-metastatic milieu even before tumor cells arrive.

Kupffer cells, the liver’s resident macrophages and the largest tissue-resident macrophage population in the body, are central players in this process. Pancreatic cancer-derived exosomes enriched in macrophage migration inhibitory factor are preferentially taken up by Kupffer cells, triggering TGF-β secretion that activates hepatic stellate cells to produce fibronectin, recruiting bone marrow-derived macrophages and neutrophils and initiating a fibrotic, immunosuppressive niche. Highly metastatic colorectal cancer cells secrete CXCL16, which binds CXCR6 on Kupffer cells and activates PI3K/AKT1/FOXO3a signaling, transcriptionally upregulating CD206 and driving M2 polarization. These M2-like Kupffer cells then secrete CXCL16 in a positive feedback loop, further entrenching the pro-metastatic phenotype. Gut microbiota composition directly influences this process: Bacteroides vulgatus enrichment increases Kupffer cell proliferation and reduces metastasis, whereas Proteus mirabilis expansion decreases Kupffer cell numbers and creates a permissive environment.

The immune cell landscape of the pre-metastatic liver undergoes equally dramatic remodeling. Natural killer cells, which constitute 30 to 50 percent of hepatic lymphocytes, normally enforce disseminated tumor cell dormancy through IFN-γ signaling. But during niche maturation, their numbers contract and cytotoxicity declines. Colorectal cancer-derived extracellular vesicles downregulate NKG2D on NK cells without altering their numbers, abrogating tumor surveillance. The HLA-E:CD94-NKG2A checkpoint enables circulating tumor cells to escape NK killing by suppressing cytotoxic granule release. Orosomucoid 2, upregulated in the pre-metastatic liver, binds ACVR1 on NK cells and activates Hippo signaling, suppressing the serine and one-carbon metabolism essential for NK cytotoxicity. Meanwhile, myeloid-derived suppressor cells expand under chronic inflammation and are recruited to hepatic sinusoids, where they establish a dominant immunosuppressive compartment through production of iNOS, reactive oxygen species, arginase-1, TGF-β, and IL-10.

Neutrophils add another layer of complexity. Tumor-derived GM-CSF converts antitumor neutrophils to a pro-tumor state via AKT-NF-κB-NFAT5 signaling, and these neutrophils accumulate in hepatic sinusoids and release neutrophil extracellular traps upon CXCR2 ligand stimulation. NET-derived elastase activates ERK in colorectal cancer cells, promoting proliferation and metastatic colonization. Fusobacterium nucleatum triggers NET formation through TLR4-ROS and NOD1/2 signaling, and high Fusobacterium tissues show greater neutrophil infiltration and NET burden. In pancreatic cancer liver metastasis, P2RX1-negative neutrophils with elevated Nrf2 and metabolic reprogramming toward oxidative phosphorylation potently suppress CD8-positive T cells in a PD-L1/PD-1-dependent manner.

The review also surveys emerging diagnostic biomarkers that could detect the pre-metastatic niche before overt metastasis. Exosomal microRNAs including miR-122, miRNA panels, and miR-6803-5p correlate with TNM staging and enable earlier detection than imaging. Elevated circulating neutrophil extracellular traps predict liver metastasis risk in early breast cancer, with NET-DNA binding CCDC25 and activating ILK-β-parvin signaling. Peripheral monocyte count independently predicts liver metastasis in colorectal cancer across a cohort of 7,187 patients. Lipopolysaccharide-binding protein drives intrahepatic fibrotic pre-metastatic niche formation via TLR4/NF-κB and serves as a candidate marker for gastric cancer liver metastasis. A random-forest model combining lactate dehydrogenase, CA19-9, ALT, CEA, total bilirubin, and the albumin-to-globulin ratio predicted liver metastasis in a cohort of 865 colorectal cancer patients.

On the therapeutic front, the review catalogs a range of preclinical interventions targeting the gut-liver axis. The SGK1 inhibitor GSK-650394 reduces IL-6/STAT3-mediated NET formation and polymorphonuclear myeloid-derived suppressor cell infiltration. Galunisertib, a TGF-β receptor I kinase inhibitor, blocks TGF-β/Smad signaling and attenuates hepatic fibrosis in gastric cancer liver metastasis models. The FXR agonist obeticholic acid reduces hepatic inflammation and reverses the immunosuppressive liver microenvironment in colorectal cancer models. A galactose-targeted lipid-calcium-phosphate nanocarrier delivering miR-122 regulates metastasis-associated genes and increases the CD8-positive to CD4-positive T-cell ratio. Dietary interventions including inulin and cellulose expand beneficial taxa and restore short-chain fatty acid production, while sodium butyrate supplementation reduces hepatic regulatory T cells and increases NKT and Th17 cells in colorectal cancer liver metastatic mice.

The authors caution that most mechanistic evidence derives from colorectal cancer, and the dominant taxa identified — Fusobacterium nucleatum, tumor-resident Escherichia coli, Proteus mirabilis, and Bacteroides vulgatus — are specific to colorectal cancer-associated dysbiosis. Features such as gut vascular barrier disruption and secondary bile acid accumulation appear broadly relevant, but the specific microbial signatures and cellular effectors in gastric, pancreatic, breast, and lung cancer are less well defined. Cross-tumor extrapolation should be cautious until equivalent multi-omic and gnotobiotic evidence is available for other primary sites. The review also notes that the pre-metastatic liver may serve as the soil in which dormant tumor cells persist for years before reactivating, raising the possibility that microbiota-targeted interception should be considered not only at the stage of radiologically detectable metastases but also during the dormancy window when disease is clinically occult but the hepatic microenvironment remains conditioned.

Subject of Research: The role of the gut-liver axis, including microbial dysbiosis, metabolite signaling, and hepatic immune cell reprogramming, in the formation of the liver pre-metastatic niche and emerging therapeutic strategies.

Article Title: Gut-liver axis in liver pre-metastatic niche formation: immune networks, microbial, and metabolic and emerging therapeutic opportunities

Article References: Zhao, L., Lin, Q., Zhang, D., Liu, Y., Zong, M., Xi, L., Xie, F., Song, S., Xue, P., Zhu, S., & Chu, X. (2026). Gut-liver axis in liver pre-metastatic niche formation: immune networks, microbial, and metabolic and emerging therapeutic opportunities. Frontiers in Microbiology, 17, Article 1931054. https://doi.org/10.3389/fmicb.2026.1931054

Image Credits: AI Generated

DOI: 10.3389/fmicb.2026.1931054

Keywords: gut-liver axis, pre-metastatic niche, liver metastasis, gut microbiota, bile acids, Kupffer cells, neutrophil extracellular traps, myeloid-derived suppressor cells, colorectal cancer, exosomal microRNAs, immune suppression, microbiota-targeted therapy