Colorectal Cancer and the Microbiome: Emerging Evidence

Colorectal cancer (CRC) is the second most lethal malignancy globally, and while genetic predisposition accounts for approximately 35% of risk, the microbiome is increasingly recognized as both a contributor to carcinogenesis and a potential therapeutic target. The spatial and temporal relationship between specific microbiome signatures and CRC development positions microbiome analysis as a future screening and risk stratification tool.

Oncogenic Microbial Signatures

Three organisms are most strongly implicated in CRC pathogenesis:

Fusobacterium nucleatum: Adheres to E-cadherin via FadA adhesin, activating Wnt/β-catenin signaling and driving epithelial proliferation. Present in 10-90× higher abundance in CRC tissue versus adjacent normal mucosa. F. nucleatum abundance in tumor tissue correlates with recurrence risk and shorter survival (Mima et al., JAMA Oncol, 2016).

Bacteroides fragilis (enterotoxigenic, ETBF): Produces fragilysin (BFT), which cleaves E-cadherin, activates NF-κB, and drives IL-8-mediated neutrophil recruitment and STAT3 phosphorylation — promoting colonic epithelial oncogenesis.

Peptostreptococcus anaerobius: Recently identified as promoting CRC through cholesterol-dependent mechanisms, stimulating cell proliferation via PCNA and Ki-67 upregulation.

Protective Microbiome Features

Faecalibacterium prausnitzii is dramatically depleted in CRC — its butyrate production induces apoptosis in colorectal cancer cell lines and its anti-inflammatory MAM molecule counters pro-oncogenic NF-κB activation. High butyrate producer abundance in the colon is associated with reduced CRC risk in prospective cohorts. See our F. prausnitzii article.

Microbiome as Diagnostic Tool

Stool microbiome signatures distinguish CRC from healthy controls with AUC 0.84 in discovery cohorts. F. nucleatum DNA in stool is being evaluated as a non-invasive CRC screening biomarker. While not yet standard of care, the field is advancing rapidly toward microbiome-guided screening adjuncts to colonoscopy and FIT testing.

Related: Dysbiosis and Disease · Short Chain Fatty Acids · Faecalibacterium prausnitzii