Colorectal cancer (CRC) is the third most common malignant tumor worldwide, with over one million newly diagnosed cases annually and a rising trend (Figure 1A). Its incidence is significantly higher in China, Europe, and North America compared to the global average (Figure 1D). Disease risk increases sharply with age, with a significant rise in incidence after 50–55 years and mortality after 45–50 years (Figure 1C). Due to improved living standards and lifestyle changes in China, CRC incidence and mortality continue to increase (Figure 1B). According to 2022 Chinese cancer statistics, CRC ranks second in incidence and fourth in mortality among malignant tumors, with approximately 517,100 new cases and 240,000 deaths annually (Han et al., 2024). F. nucleatum is a core microorganism in oral dental plaque (Bolstad et al., 1996; Borisy and Valm, 2021), widely distributed in the human digestive system, reproductive system, and other sites. It is associated with various diseases, including periodontitis, pancreatitis, CRC, pelvic inflammatory disease, and adverse pregnancy outcomes (Han, 2015; Swidsinski et al., 2011; Xu and Han, 2022). Multiple studies indicate significantly elevated F. nucleatum abundance in CRC tissue and fecal samples, suggesting its close association with CRC development (Castellarin et al., 2012; Wong and Yu, 2019). The detection rate of this bacterium in CRC tissues is much higher than in normal tissues, indicating its potential as a diagnostic biomarker or therapeutic target.

As a Gram-negative anaerobic bacterium, F. nucleatum plays a critical role in CRC initiation, recurrence, metastasis, and drug resistance. It participates in CRC progression through mechanisms such as activating inflammatory responses, promoting tumor cell proliferation and invasion, and inducing resistance to chemotherapy and immunotherapy. Systematic studies on F. nucleatum abundance in intestinal tissues and related molecular expressions are valuable for elucidating CRC pathogenesis, optimizing diagnostic and therapeutic strategies, and assessing prognosis. Existing reviews often focus on basic research and lack clinical guidance. This study integrates the association, pathogenic mechanisms, and clinical applications of F. nucleatum and CRC, constructing a review framework with both theoretical depth and clinical practicality to inform CRC precision medicine. The study emphasizes the following directions: (1) exploring interactions between F. nucleatum, intestinal microbiota, and host factors; (2) developing targeted therapeutic strategies against F. nucleatum; (3) promoting standardization of detection methods and normalization of data analysis to ensure scientific rigor and reproducibility. These efforts will provide new insights for personalized CRC treatment and ultimately improve patient survival and prognosis.

To systematically review research progress on F. nucleatum in colorectal cancer, this study employed a structured literature search approach. Databases searched included PubMed, Embase, Web of Science, and China National Knowledge Infrastructure (CNKI), with a search period from 1 January 2010, to 30 June 2024. A combined keyword strategy was used: (“Fusobacterium nucleatum” OR “F. nucleatum”) AND (“colorectal cancer” OR “CRC”) AND (“diagnosis” OR “therapy” OR “prognosis”). Inclusion criteria were as follows: (1) original research papers; (2) provision of explicit detection methods or clinical data; (3) sample size ≥ 50 cases. Exclusion criteria were as follows: (1) reviews, conference abstracts, or case reports; (2) non-human studies; (3) duplicate published data. Finally, the included literature underwent independent screening and cross-validation by two researchers.

F. nucleatum belongs to the family Fusobacteriaceae. This bacterium is anaerobic but can still grow in environments with oxygen levels up to 6% (Bolstad et al., 1996). Early observations in the human oral cavity identified fusiform microorganisms, and the Fusobacterium genus was isolated based on sensitivity to dyes and antibiotics (Baird-Parker, 1957). Active strains that ferment amino acids, produce acetate and butyrate, and exhibit limited sugar-degrading activity are classified as F. nucleatum (Yu et al., 2022). Subsequent studies on 16S genomics have suggested that the common ancestor of Fusobacterium was Leptotrichia, which underwent adaptive radiation during evolution, diverging into three main lineages and five major clades (Manson McGuire et al., 2014). Based on 16S rRNA gene sequence analysis, it can be further classified into four subspecies: nucleatum, animalis, vincentii (including fusiforme), and polymorphum (Nie et al., 2015). These subspecies have been found in clinical tissues and fecal samples of patients with CRC, with a significant increase in F. nucleatum (Bi et al., 2022; Table 1).

In the intestinal tract, F. nucleatum forms complex interactions with host microbiota, influencing its colonization and pathogenicity, thereby affecting gastrointestinal immunity and metabolism. When microbial diversity is high and butyrate-producing bacteria (e.g., Faecalibacterium, Roseburia) are abundant, F. nucleatum struggles to obtain sufficient nutrients and adhesion sites. However, microbiota dysbiosis caused by antibiotics, high-fat diets, or inflammatory bowel disease (IBD) weakens the “colonization resistance” of commensal bacteria, providing a window for F. nucleatum colonization (Dewan et al., 2025). Evidence from the oral-intestinal axis indicates that F. nucleatum can form “corncob-like” co-aggregates with oral resident bacteria Streptococcus sanguinis, utilizing its filamentous structure to more easily penetrate the mucus layer and colonize colorectal mucosa (Sun et al., 2019). F. nucleatum can exploit ornithine (ArcD-dependent) excreted by Streptococcus gordonii as a nitrogen source, accelerating its own proliferation (Sun et al., 2019). F. nucleatum acts as a bridge between early and late colonizers in dental plaque by forming biofilms (Borisy and Valm, 2021). Signaling molecules from P. gingivalis can accelerate F. nucleatum biofilm formation (Yamaguchi-Kuroda et al., 2023). In biofilm form, F. nucleatum exhibits enhanced virulence and invasiveness, enabling it to invade multi-layered epithelial collagen matrices and survive under aerobic conditions (Gursoy et al., 2010), thereby disrupting gastrointestinal immune and metabolic homeostasis.

Studies have confirmed that F. nucleatum participates in the formation, progression, and treatment response of colorectal cancer through a series of complex mechanisms (Figure 2).

Firstly, F. nucleatum binds to colorectal epithelial cells via adhesin FadA and E-cadherin, promoting tumor cell proliferation and invasion (Manson McGuire et al., 2014; Rubinstein et al., 2013). Gal-Gal-NAc overexpression in colorectal cancer enables F. nucleatum recognition and binding, leading to its accumulation in tumor tissues (Abed et al., 2016). F. nucleatum abundance changes are significant in colorectal cancer patients, highlighting its potential as a biomarker for screening and diagnosis (Kwong et al., 2018; Liang et al., 2020; Lin et al., 2022; Yu J. et al., 2017). It also reduces m⁶A modification in CRC cells, enhancing invasiveness (Chen et al., 2022), shifts central carbon metabolism in tumor cells, and promotes CRC cell invasion (Ternes et al., 2022). F. nucleatum activates TLR4 signaling, leading to NF-κB activation and increased miR-21 expression, which promotes tumor metastasis (Yang et al., 2017).

Secondly, F. nucleatum activates inflammatory responses and immune evasion, inhibiting host immune responses and promoting tumor development. It induces pro-inflammatory factors such as NF-κB, IL-6, and IL-8 (Queen et al., 2021; Rubinstein et al., 2013), increases inflammation-related gene expression (Galeano Niño et al., 2022), and exists in immunosuppressive microecological niches, reducing CD4 and CD8 levels while upregulating CD66b+, ARG1, and CTLA4 (Galeano Niño et al., 2022). F. nucleatum’s Fap2 protein interacts with the inhibitory receptor TIGIT on NK and T cells (Gur et al., 2015), and upregulates PD-L1 expression in CRC cell lines, promoting immune evasion (Galeano Niño et al., 2022; Gao et al., 2023).

Additionally, F. nucleatum influences the tumor microenvironment by regulating angiogenesis and metastasis. Inflammatory responses induce IL-1β production, which activates endothelial cells to produce pro-angiogenic factors, promoting angiogenesis and tumor progression (Jagielska et al., 2012; Nakao et al., 2005). F. nucleatum alters miRNA and chemokine expression in host cells, delivered via exosomes, increasing cell migration and tumor metastasis (Guo et al., 2020). It also upregulates KRT7-AS, regulating CRC cell lymph node migration (Chen et al., 2020, 2022). Regarding treatment, F. nucleatum levels correlate with colorectal cancer treatment response. Increased F. nucleatum levels are associated with improved response to PD-L1 blockade therapy, possibly by activating STING signaling and increasing PD-L1 expression (Gao et al., 2021). However, F. nucleatum may also impair CD8⁺ T cell immunity, reducing sensitivity to anti-PD-1 mAb and increasing immunotherapy resistance (Jiang et al., 2023). It initiates protective autophagy via the TLR4 pathway, enhancing chemotherapy resistance (Zheng et al., 2019).

F. nucleatum promotes CRC progression through dual mechanisms: (1) F. nucleatum mediates signaling pathways, including the FadA/E-cadherin/β-catenin regulatory axis and METTL3/m⁶A modification, to regulate CRC proliferation and invasion capabilities, thereby directly influencing CRC progression; (2) F. nucleatum induces the production of pro-inflammatory factors such as NF-κB, IL-6, and IL-8 while modulating PD-L1 expression to affect inflammatory and anti-tumor immune responses, thereby indirectly regulating CRC progression.

Recent advances in genetic technologies have significantly deepened the understanding of F. nucleatum-CRC association mechanisms. At the genomic level, whole-genome sequencing and functional annotation revealed key differences among subspecies: for example, the F. animalis genome harbors a unique fnp gene cluster closely associated with its tumor metastasis-promoting capacity, while the nucleatum subspecies (F. nucleatum) carries more adhesin genes related to oral colonization. Comparative genomic analysis further identified differentially expressed genes among subspecies (e.g., fadA adhesin, gal-galNAc receptor) that directly influence their pathogenic potential in the intestine (Ma et al., 2023; Queen et al., 2021). At the transcriptomic level, RNA sequencing has constructed high-resolution global RNA profiles of Fn subspecies during early, mid-exponential, and early stationary growth phases, aiding in elucidating functional characteristics at different disease progression stages (Ponath et al., 2021).

In multi-omics integration, combining transcriptomics and metabolomics revealed that Fn promotes cell proliferation by modulating amino acid biosynthesis, central carbon metabolism, protein digestion/absorption, and other metabolic pathways in CRC cells (Wu et al., 2023). At the genetic engineering level, tools including CRISPR interference (CRISPRi) systems, suicide plasmid-based gene inactivation systems, replicative plasmid-based gene expression control systems, and transposon-based random mutagenesis systems have become critical strategies for studying Fn pathogenicity. These tools enabled targeted silencing of key virulence genes (e.g., fadA, gal-galNAc), facilitating validation of their roles in tumor cell adhesion and invasion (Guan et al., 2025; Zhou et al., 2024). The establishment of these genetic tools not only clarified subspecies-specific pathogenic mechanisms (e.g., F. animalis exhibits significantly stronger metastasis-promoting capacity than F. nucleatum) but also advanced the development of precision intervention strategies against F. nucleatum, such as subspecies-specific antigen-based vaccine design and inhibitors targeting key metabolic pathways. Integrating multi-omics technologies with organoid models holds promise for further dissecting the dynamic microbiota-host interaction network, providing novel targets for CRC precision medicine.

Quantitative and localization analysis of F. nucleatum is a significant direction in current colorectal cancer research. It aims to deepen the understanding of its role in the occurrence and development of colorectal cancer and may also provide new strategies for future diagnosis and treatment. Currently, commonly used methods for detecting F. nucleatum include culture, PCR, qPCR, FISH, FIT, etc. PCR can determine the presence and abundance of F. nucleatum by detecting its specific genes or 16S rRNA sequences. The diagnostic workflow consists of three stages: (1) sample preprocessing; (2) quantitative PCR (qPCR) using FadA gene-specific primers; and (3) bioinformatics analysis. The application process is shown in Figure 3.

The high enrichment of F. nucleatum in colorectal cancer tissues suggests its role in cancer development. Its abundance correlates with malignancy grade, clinical stage, and prognosis, with high levels indicating poorer prognosis and higher recurrence risk. F. nucleatum enhances cancer cell stemness, invasion, and metastasis, promoting tumor progression. It also affects the tumor microenvironment and regulates immune cell function and distribution. While the correlation is significant, the specific mechanism is not fully understood (see Table 3 for more information). Future research should explore F. nucleatum’s role in cancer development, its interactions with the tumor microenvironment and immune system, and develop targeted therapeutic strategies. A deeper understanding will provide new insights and methods for colorectal cancer diagnosis and treatment.

F. nucleatum plays a pivotal role in CRC chemotherapy. Studies indicate that F. nucleatum significantly promotes the development of chemotherapy resistance in colorectal cancer. F. nucleatum facilitates CRC resistance by activating autophagy and inhibiting pyroptosis and ferroptosis (Li et al., 2024; Wang et al., 2024; Yu T. et al., 2017). Additionally, F. nucleatum promotes the secretion of hsa_circ_0004085 via exosomes, influencing endoplasmic reticulum stress and thereby enhancing chemotherapy resistance in CRC (Hui et al., 2024).

With the widespread application of immunotherapy in colorectal cancer, the association between F. nucleatum burden and treatment efficacy has become a research focus. Recent studies reveal a bidirectional regulatory relationship between F. nucleatum load and response to immune checkpoint inhibitor (ICI) therapy: on one hand, it upregulates PD-L1 expression through m⁶A modification of IFIT1 or activation of the STING pathway, while recruiting IFN-γ⁺CD8⁺ tumor-infiltrating lymphocytes (TILs), thereby enhancing tumor sensitivity to PD-L1 therapy (OR = 3.82, 95% CI 1.25–11.7) (Gao et al., 2021, 2023); on the other hand, succinate produced by the bacterium reduces levels of IFN-γ, TNF-α, and chemokines such as CCL5/CXCL10 in the tumor microenvironment, inhibiting CD8⁺ T cell infiltration and leading to resistance against anti-PD-1 monoclonal antibodies (HR = 2.14, 95% CI 1.07–4.28) (Jiang et al., 2023). This contradictory phenomenon may relate to differences in F. nucleatum colonization sites, which drive activation of distinct intracellular and extracellular signaling pathways in CRC, resulting in opposing immunotherapeutic regulatory effects.

Given the critical role of F. nucleatum in CRC chemotherapy and immunotherapy resistance, studies have begun exploring F. nucleatum-targeted therapeutic strategies to enhance treatment sensitivity. Research indicates that antibiotic treatment with metronidazole can reduce intestinal F. nucleatum and restore immunotherapy sensitivity (Jiang et al., 2023; Wang et al., 2023). Oral or intravenous administration of azide-modified phage covalently linked to dextran nanoparticles, which inhibit F. nucleatum growth, significantly improves the efficacy of first-line CRC chemotherapy (Zheng et al., 2019). The use of tubercidin I (TBI) simultaneously enhances dendritic cell (DC) vaccine efficacy and suppresses F. nucleatum infection, thereby improving immunotherapy outcomes (Tong et al., 2023). The development of F. nucleatum-targeted therapeutic approaches holds promise for reducing CRC resistance.

Beyond its critical role in CRC drug resistance, F. nucleatum also demonstrates clinical potential in monitoring treatment efficacy, post-therapy recurrence rates, and mortality. F. nucleatum is significantly associated with poor response to chemotherapy/immunotherapy, increased post-treatment recurrence, and elevated patient mortality in CRC (Jiang et al., 2023; Wang et al., 2024; Yu T. et al., 2017). Studies indicate that F. nucleatum significantly elevates chemotherapy-specific mortality in colon cancer patients [hazard ratio (HR) = 1.92, 95% confidence interval (CI): 1.07–3.45] (Borozan et al., 2022); F. nucleatum positivity markedly increases recurrence risk in chemotherapy-treated CRC patients (HR = 7.5, 95% CI: 3.0–19.0; P < 0.001) (Serna et al., 2020).