The gut microbiome and potential implications for early-onset colorectal cancer

Figures & data

Table 1. Microbiome and specific bacteria studies focusing on association with oncogenesis, risks and mechanisms of carcinogenesis, immunomodulation and therapy responses.

Bacterium	Disease, population, (n = population size) and major findings	Ref.
Fusobacterium species	CRC, Human (n = 95 carcinoma/normal colon pairs) CRC is enriched with Fusobacterium species, especially phylotypes similar to F. nucleatum, F. mortiferum and F. necrophorum evidenced by 16S rDNA sequencing in tumors and with FISH probes for Fusobacterium in CRC No correlation noted between F. nucleatum amount and age	[48]
Fusobacterium species F. nucleatum	CRC, Human (n = 99 carcinoma/normal colon pairs) F. nucleatum is over-represented in CRC tumor specimens compared with normal controls by quantitative PCR (p = 2.52 × 10^-6) Subjects with higher proportion of Fusobacterium were more likely to have regional lymph node metastasis (p = 3.5 × 10^-3) No correlation noted between F. nucleatum amount and age	[49]
F. nucleatum	CRC, Human (n = 84) F. nucleatum stimulates proliferation of human CRC cells with FadA (virulence factor) by adhering to and invading E-cadherin-expressing CRC cells (p < 1.0 × 10^-3) FadA complexes activate E-cadherin-mediated cellular signaling and proliferation via β-catenin-regulated transcription (p < 1.0 × 10^-3) CRC and precancerous adenoma patients have elevated FadA gene colonic expression compared with healthy patients (p < 1.0 × 10^-3) Mice xenografts (n = 30) FadA promoted E-cadherin-mediated CRC growth and inflammation in vivo (p < 1.0 × 10^-3)	[56]
F. nucleatum	CRC, Human (n = 86) F. nucleatum is enriched (PCR of stool) in CRC patients (p < 1.0 × 10^-5) and those with adenomas (p < 5.0 × 10^-3) compared with healthy controls F. nucleatum-positive CRC is enriched with proinflammatory gene expression Mice F. nucleatum accelerated tumorigenesis in mice with mutation in one copy of tumor-suppressor gene APC or genetic defects resulting in chronic inflammation (p < 1.0 × 10^-4) (n = 12) F. nucleatum expands myeloid-derived immune cells but not lymphoid immune cells in tumor microenvironment (p < 1.0 × 10^-3) (n = 15)	[60]
Fusobacterium species	CRC, Human (n = 310) Fusobacterium is detectable in 74% (111/149) of CRC tissues and heavily enriched in 9% (14/149) F. nucleatum exhibits 3600-fold and pan-Fusobacterium exhibits 250-fold enrichment in CRC compared with adjacent normal mucosa (both p-values <1.0 × 10^-4) Fusobacterium-high CRC was associated with CIMP positivity (p = 1.0 × 10^-4), TP53 wild-type (p = 1.5 × 10^-3), hMLH1 methylation present (p = 2.8 × 10^-3), MSI (p = 1.8 × 10^-2), CHD7/8 mutation present (p = 2.0 × 10^-3). Data showed high Fusobacterium level had distinct molecular pattern and high rate of mutations overall, thus suggesting pathogenic rather than passenger role Median age of patients of whose CRCs were studied was over 60 years and a significant trend toward F. nucleatum-high status and patient age greater than 70 (p = 0.09) was noted	[50]
F. nucleatum	CRC, Human (n = 598) F. nucleatum-positive CRC were inversely associated with CD3^+ T-cell density (p = 6.0 × 10^-3) No correlation noted between F. nucleatum-status and age (mean age of all patients was 67.2 ± 8.4 years with mean ages of 67.2 ± 8.5, 67.7 ± 7.4 and 6.68 ± 7.3 in F. nucleatum negative, low and high CRC (p = 0.89)	[53]
F. nucleatum	CRC, Human (n = 1069) Higher levels of F. nucleatum in CRC tissue were associated with decreased survival (HR for cancer-specific mortality in F. nucleatum-low vs -high CRC were 1.25 and 1.58, respectively [p = 0.02]) No correlation noted between F. nucleatum-status and age (mean age of all patients was 69.3 ± 8.8 years with mean ages of 69.2 ± 8.8, 71.1 ± 9.0 and 68.8 ± 8.3 in F. nucleatum negative, low and high CRC [p = 0.21])	[62]
F. nucleatum	CRC, Human (n = 98) F. nucleatum activates β-catenin signaling via TLR4/P-PAK1/P-β-catenin S65 cascade (p < 0.05) No correlation noted between F. nucleatum-status and age (mean age: 59.4 vs 58.0 for F. nucleatum-negative vs -positive CRC, respectively [p = 0.281])	[58]
F. nucleatum	CRC, Human CRC cell lines and mice xenografts F. nucleatum promotes CRC proliferation and invasion in CRC cell lines (p < 1.0 × 10^-3 to 0.05) (n = 3) and mouse xenograft animal models (p < 0.01) (n = 15) F. nucleatum promotes tumorigenesis in APC^Min/+ mice (p < 0.05) (n = 10) F. nucleatum promotes tumor proliferation through miRNA-21 and MAPK signaling pathway (p < 0.05) (n = 8 mice) Human (n = 125) Tumors with high amounts of F. nucleatum DNA and miRNA-21 had shorter survival times	[59]
F. nucleatum	CRC, Human (n = 11 primary CRCs and paired liver metastases and n = 201 primary liver tumors) Fusobacterium is viable and migrates with CRC to distant metastasis sites such as liver, suggesting the microbiota are intrinsic and essential to the microenvironment Fusobacterium is rare in primary liver carcinoma and enriched in liver metastases from CRCs compared with primary liver carcinoma (p = 8.0 × 10^-3) Human cell lines and mice xenografts Fusobacterium survives in CRC PDXs through multiple generations (n = 1) Treatment of Fusobacterium-positive PDX model with metronidazole decreases Fusobacterium load and tumor growth (p = 2.0 × 10^-3 for both) (n = 47)	[61]
F. nucleatum	CRC, Human (n = 1019) Prudent diet score was associated with lower risk of F. nucleatum-positive cancers (p = 3.0 × 10^-3) No significant trend noted with prudent diet and F. nucleatum-negative cancer and no significant heterogeneity between F. nucleatum-status CRC in relation to Western dietary pattern scores	[54]
F. nucleatum	CRC, Human (n = 92 in F. nucleatum and recurrence study and n = 173 in validation study for prediction value) F. nucleatum is enriched in recurrent CRC tissue as compared with nonrecurrent CRC (p < 0.01), suggesting it plays a role in recurrence and is an independent predictor of CRC aggressiveness F. nucleatum promotes cancer autophagy activation (p < 0.05) to induce chemotherapy resistance	[51]
F. nucleatum	CRC, Human (n = 1041) Association of F. nucleatum with TIL varies by MSI status In MSI-H CRC, presence of F. nucleatum was negatively associated with TILs (OR: 0.45; CI: 0.22–0.92) In non-MSI-H CRC, presence of F. nucleatum was positively associated with TILs (OR: 1.91; CI: 1.12–3.25)	[92]
F. nucleatum	CRC, Human CRC cell lines F. nucleatum stimulates CRC growth in in vitro model via Annexin A1 (modulator of Wnt/β-catenin signaling) (p < 1.0 × 10^-3 to <0.05) (multiple cell line experiments performed in triplicates and repeated three- to four-times) Expression of Annexin A1 expression in CRC is a predictor of poor prognosis (p < 1.0 × 10^-3) (n = 466) Proposed ‘two-hit’ model where a somatic mutation serves as the first hit and F. nucleatum serves as the second hit based on a positive feedback loop seen between FadA and Annexin A1 that was absent in noncancerous cells	[57]
F. nucleatum	CRC, Human (n = 593) In stage II/III CRC treated with adjuvant therapy, prognostic value of F. nucleatum depends on tumor location and MSI status Disease-free survival was improved in F. nucleatum-high CRC with nonsigmoid CRCs (p = 2.6 × 10^-2) In multivariate analysis, F. nucleatum was an independent favorable prognostic factor for nonsigmoid CRC (HR: 0.42; CI: 0.18–0.97, p = 4.3 × 10^-2) only in non-MSI-H subset (p = 1.4 × 10^-2) No correlation noted between F. nucleatum-status and age (41.2 vs 58.8% of F. nucleatum-high CRCs were younger than 59 vs ≥59 years, respectively, and 45.8 vs 54.2% F. nucleatum-low/-negative CRCs were younger than 59 vs ≥59 years, respectively) (p = 0.286)	[93]
B. fragilis	CRC, Human cell lines bft activates T-cell factor dependent β-catenin nuclear signaling and c-myc expression resulting in colonic cell transformation suggesting the potential to contribute to oncogenesis (n = 4)	[67]
B. fragilis	CRC, Human (n = 132) First study demonstrating increase of ETBF in CRC patients bft was detected by PCR in stool samples of 38% CRC patients compared with 12% control patients (p = 9.0 × 10^-3)	[65]
B. fragilis	CRC, Mice ETBF activates Stat3 (n = 13 mice) and induces T-helper cell-type 17 inflammatory infiltrates (n = 3–5 mice per group and experiments repeated two- to three-times) and demonstrated a role for endogenous T-cell immune responses in carcinogenesis	[68]
B. fragilis	CRC, Human (n = 98) Mucosa of CRC patients are more often bft-positive than controls (p = 0.04) Late-stage CRC had trend of increased bft positivity compared with early-stage CRC (100 vs 72.7%, p = 9.3 × 10^-2)	[66]
B. fragilis	CRC, Mice (n = 70) Oral administration of low-dose recombinant BFT-2 inhibited carcinogenesis (p < 0.05)	[70]
B. fragilis	CRC, Human cell lines PSA from B. fragilis induces IL-8 via TLR-2 and suppresses migration and invasion of CRC (p < 0.05) (n = 3 experiments)	[71]
S. gallolyticus	CRC, Human (n = 141) S. gallolyticus is presented at higher rates in CRC (20.5% in CRC with bacteremia, 17.3% without bacteremia) compared with control tissues (2%) (p < 0.05) CRC tissue was associated with higher expression (mRNA ratios compared with controls) of IL-1 (1.77), COX-2 (1.63), IL-8 (1.73) (p < 0.05) No correlation noted between detection of S. gallolyticus and age (mean age in controls, CRC without bacteremia and CRC with bacteremia were 57.4 ± 4.7, 59.22 ± 8.13 and 56.6 ± 6.7, respectively) (p = 0.41)	[74]
S. gallolyticus	CRC, Human cell lines S. gallolyticus promotes colon cancer proliferation (p < 0.05) and the effect is dependent on bacterial growth phase (p < 0.05), direct contact between live bacteria and responsive cells (p < 0.05) (cell lines tested with duplicate wells and experiments repeated at least three-times), and β-catenin pathway (p < 0.01) (n = 3 experiments) Mice xenografts S. gallolyticus promoted tumor growth in xenograft models (p < 0.05) (n = 10) Mice (n = 19) S. gallolyticus promotes tumorigenesis in AOM-induced mouse models of CRC (p < 0.05) via β-catenin pathway	[75]
S. gallolyticus	CRC, Mice S. gallolyticus colonization is 1000-fold higher in genetically-prone tumor-bearing mice compared with normal mice (p < 0.01) (n = 17) S. gallolyticus-specific bacteriocin kills commensal gut enterococci in vitro and bile acids enhance this bacteriocin in vivo resulting in increased S. gallolyticus colonization (<0.05). Wnt pathway activation and increased intestinal bile acids create optimal environment for S. gallolyticus colonization	[76]
S. gallolyticus	CRC, Humans (n = 8126) There is a higher risk for CRC in patients who have positive antibody response to S. gallolyticus pilus protein Gallo2178 (OR: 1.23; CI: 0.99–1.52, not statistically significant) with stronger association for cases diagnosed less than 10 years from blood draw (OR: 1.40; CI: 1.09–1.79) compared with those diagnosed more than 10 years from blood draw (OR: 0.79; CI: 0.50–1.24)	[78]
H. pylori	Gastric cancer, Humans (n = 795) Pre-neoplastic gastric lesions regress as a function of the square of H. pylori-negative time Patients who were H. pylori-negative at 12 years experienced 14.8% more regression and 13.7% less progression of pre-neoplastic lesions compared with H. pylori-positive patients at 12 years (p = 1.0 × 10^-3), suggesting patients with pre-neoplastic gastric lesions and H. pylori infection should be treated and cured of infection	[81]
H. pylori	CRC, Humans (n = 384) Meta-analysis of 11 human studies estimated an OR of 1.4 (CI: 1.1–1.8) for association of H. pylori to CRC	[84]
H. pylori	Gastric cancer, Humans (n = 403) H. pylori eradication in precancerous tissue resulted in regression of gastric atrophy (62% regression in antrum and 36% in corpus) when compared with non-H. pylori-eradicated cases (31% regression in antrum and 13% in corpus) (p < 1.0 × 10^-4) over 2.5 years No regression of intestinal metaplasia was seen with H. pylori treatment over 4.5 years, but progression of intestinal metaplasia was more rapid in non-H. pylori-eradicated versus eradicated cases (p < 0.05)	[82]
H. pylori	CRC, Humans (n = 7679) Meta-analysis of nine human studies estimated OR: 0.18 (CI: 0.99–1.40) (p > 0.05) for association between H. pylori infection and CRC risk No statistical association between H. pylori infection and colorectal neoplasm risk was found OR for H. pylori infection and adenomas was 1.8 (CI: 1.35–2.51) (p < 0.01), thus H. pylori may increase risk of developing colorectal adenomas	[85]
General microbiome	PDA, Humans (n = 12) PDA harbors more microbiome with select bacterial profile compared with normal pancreas and normal gut (p < 1.0 × 10^-4) PDA, Mice Germ-free mice and mice with PDA treated with antibiotics were protected against PDA progression (p < 0.01) (n = 8, experiments repeated five-times) Fecal transfer from PDA-bearing mice to genetically susceptible mice hosts accelerated tumorigenesis (p < 0.01) (experiment repeated three-times) Antimicrobial-ablated mice models increased intratumoral immunogenicity with increased CD8:CD4 T-cell ratio and increased expression of PD-1 (p < 0.01–0.05) (n = 10, experiment repeated five-times) Study suggested PDA microbiome programs TAMs via TLR signaling to induce immune tolerance by suppressing T-cell immunity	[87]
General microbiome	PDA, Humans (n = 43 in discovery cohort and n = 25 in validation cohort) PDA microbial diversity was higher in long-term survivors and patients with high diversity had longer survival than those with low diversity (median OS: 9.66 vs 1.66) (p = 1.6 × 10^-4) Long-term survivor PDA were enriched with Pseudoxanthomonas, Saccharopolyspora and Streptomyces Long-term survivors had greater CD3^+, CD8^+ and granzyme B^+-cell expression than short-term survivors (p = 2.73 × 10^-2, p < 1.0 × 10^-4 and p = 0.04, respectively), suggesting microbiome drives antitumor immune responses Mice Gut-tumor microbiome cross-talk exists. Human-to-mouse FMT from human short-term survivors into mice with orthotopic syngeneic tumors showed a small proportion (5%) of mice tumor-harbored human donor microbiome Human-to-mouse FMT from long-term survivors reduced tumor growth and enriched tumors with activated T-cell infiltration relative to FMT from short-term survivors or healthy donors (p < 1.0 × 10^-3)	[88]
General microbiome	Melanoma, Humans (n = 43) Melanoma patients undergoing anti-PD-1 therapy who were responders showed higher alpha diversity (p < 0.01) and relative increase in Ruminococcaceae family (p < 0.01) Mice A ‘favorable’ gut microbiome (e.g., high diversity and abundance of Ruminococcaceae/Faecalibacterium) is associated with increased immune surveillance as seen by reduced tumor growth (p = 0.04) (n = 11), improved responses to anti-PD-L1 therapy (p = 0.20) (n = 7) and higher CD8^+ tumor density (p < 0.05) (n = 6) in long-term survivor human-to-mouse FMT compared with short-term survivor human-to-mouse FMT studies	[89]

AOM: Azoxymethane; bft: Entero-toxigen gene; CRC: Colorectal cancer; ETBF: Entero-toxigenic B. fragilis; FMT: Fecal microbiota transplant; HR: Hazard ratio; MSI: Microsatellite instability; MSI-H CRC: Microsatellite instability-high colorectal cancer; OR: Odds ratio; OS: Overall survival; PDA: Pancreatic ductal adenocarcinomal; PDX: Patient-derived xenograft; PSA: Polysaccharide A; TAM: Tumor-associated macrophage; TIL: Tumor-infiltrating lymphocyte; TLR: Toll-like receptor.

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