The scale of the oral ecosystem alone is striking. Based on 16S rDNA profiling, the dominant bacterial phyla in a healthy mouth, Firmicutes, Actinobacteria, Proteobacteria, Fusobacteria, Bacteroidetes, and Spirochaetes, together account for roughly 96 percent of oral bacteria. These microbes occupy distinct ecological niches, from supragingival and subgingival plaque to the tongue, buccal mucosa, saliva, and tonsils, each hosting its own characteristic community assembly. Notably, the oral microbiome shows significant variation between individuals but remarkable stability within a single person over time, exhibiting less temporal fluctuation than communities at sites like the gut or skin. That stability, the authors suggest, makes the mouth an ideal biological system for microbiome research, and potentially a reliable window into systemic health. Salivary gland function, oral clearance rates, pH, and secretory immunoglobulin A levels all act as regulators of this balance, and when any of them falter, the stage is set for dysbiosis.

Under healthy conditions, the oral community functions as a defensive barrier, resisting colonization by exogenous pathogens through competition and the inhibitory effects of microbial metabolites. But the review emphasizes that the boundary between commensal and pathogen is porous. Opportunistic species such as Porphyromonas gingivalis and Fusobacterium nucleatum, ordinarily tolerated members of the oral flora, can turn inflammatory and carcinogenic when the delicate equilibrium of the community is disrupted. In a dysbiotic state, these organisms and their metabolic products activate extracellular matrix degradation pathways and interfere with immune-related signaling, contributing to a chronic pro-inflammatory state that favors tumorigenesis. The review also connects this imbalance to acute systemic conditions, noting that oral dysbiosis has been associated with acute respiratory distress syndrome and sepsis through oral-intestinal axis-mediated changes in gut flora, underscoring that the mouth’s influence extends well beyond oncology.

Central to the review’s argument is the concept of oral-systemic axes, the routes by which oral microbes establish communication with microbial communities in distant organ systems. More than half of microbial genera can be detected in both the oral cavity and the gut, and oral organisms can migrate directly to the intestinal mucosa via the digestive tract or disseminate through the bloodstream. One vivid example involves periodontitis: pathologically activated Th17 cells acquire gut tropism, migrate to inflamed intestines, are specifically reactivated by colonized oral pathogens, and subsequently induce colitis. In the tumor context, dysbiosis, colonization, and translocation of oral bacteria upregulate cytokines and inflammatory mediators that reshape the tumor microenvironment. Metabolites play a critical role as well. Lactate can recruit immunosuppressive cell types including regulatory T cells, tumor-associated macrophages, and myeloid-derived suppressor cells, while dietary tryptophan metabolites activate the aryl hydrocarbon receptor in myeloid cells, fostering an immunosuppressive milieu that supports pancreatic ductal adenocarcinoma growth.

The mechanistic detail is deepest for colorectal cancer, where Fusobacterium nucleatum has become something of a molecular celebrity. The bacterium’s outer membrane protein Fap2 binds to the Gal-GalNAc carbohydrate abundant on colorectal tumor cells, mediating bacterial enrichment within tumors, while its adhesin A binds E-cadherin on intestinal epithelial cells and activates beta-catenin signaling, driving uncontrolled cell proliferation. F. nucleatum also induces secretion of IL-8 and CXCL1 to promote cancer cell migration, recruits tumor-infiltrating immune cells via CEACAM1 to evade immune surveillance, and targets the long non-coding RNA ENO1-IT1 to enhance glycolysis and tumor growth. Strikingly, Fusobacterium strains isolated from colorectal tumors closely resemble strains from the same patients’ saliva, supporting the hypothesis that colonic dysbiosis is at least partly seeded from the mouth. Germ-free mice transplanted with human saliva have allowed researchers to track how oral bacteria colonize the gastrointestinal tract through continuous swallowing, hematogenous spread during periodontal bacteremia, and environmental changes in the gut that permit stable colonization.

Similar patterns appear across other malignancies. In gastric cancer, oral taxa such as Rothia, Eikenella corrodens, Bergeyella, and Capnocytophaga are enriched in the gastric mucosa of patients, and Helicobacter pylori is detected in the oral cavity as well as the stomach. Actinomyces, an emerging opportunistic pathogen, promotes autophagy and upregulates TLR4 expression in gastric carcinogenesis, while acid-producing bacteria drive excessive short-chain fatty acid and lactate production that fuels tumor angiogenesis. In pancreatic cancer, epidemiological studies consistently link poor oral hygiene and periodontal disease to elevated risk, and intracellular P. gingivalis has been shown to promote oncogenic behavior in pancreatic cancer cells by activating Akt signaling. Perhaps most provocatively, pancreatic cyst fluid from tumor patients harbors a microbial community overlapping substantially with the oral microbiota, and the hypoxic, immunosuppressive pancreatic tumor environment appears to offer favorable conditions for oral anaerobes. In lung cancer, reduced oral alpha-diversity is negatively associated with risk, and P. gingivalis colonization, encouraged by long-term smoking and alcohol consumption, promotes malignant progression.

The relationship runs in both directions, and cancer treatment itself reshapes the oral ecosystem. Chemotherapy commonly induces oral mucositis and xerostomia, disrupting the homeostasis between host defenses and commensal bacteria and opening portals for opportunistic infection; studies report increases in Streptococcus viridans group species and, after two weeks of treatment, in anaerobes such as F. nucleatum and Prevotella intermedia. Radiotherapy for head and neck cancers raises the abundance of Gram-negative bacteria and Candida, increases Lactobacillus across multiple oral sites, and reduces bacterial alpha-diversity, with the most frequent complication being mucositis whose severity tracks with microbial shifts. Encouragingly, early clinical evidence suggests probiotics may mitigate this damage, with Bacteroides and Bifidobacterium genera shown to boost immune cell number and activity, potentially enhancing anti-CTLA-4 and anti-PD-L1 immunotherapy while reducing treatment toxicity.

Prognostic and diagnostic implications are already taking shape. The Fusobacterium genus has been independently linked to poorer outcomes in pancreatic, oral squamous cell, and colorectal cancers, while salivary Candida carriage correlates with unfavorable prognosis in oral cancer and Malassezia enrichment with favorable prognosis. Higher oral microbial diversity within pancreatic tumors and richer, more even oral communities in non-small cell lung cancer patients have both been associated with longer survival, and diversity indices may serve as independent predictors of overall and relapse-free survival. On the diagnostic front, the numbers are eye-catching: salivary microbiome analysis achieved diagnostic accuracy exceeding 90 percent in a cohort of 47 oral squamous cell carcinoma patients, salivary screening for gastric cancer yielded area-under-curve values of 91 and 97 percent in separate studies, and combining oral with fecal microbiome profiles improved colorectal cancer detection to 95 percent specificity and 88 percent sensitivity, outperforming the standard fecal immunochemical test.

The authors are careful to temper enthusiasm with candor. Current research remains largely observational, limited by heterogeneous study designs, insufficient causal evidence in human cohorts, and persistent challenges in standardizing oral microbiome sampling and analysis, and the prognostic literature remains inconclusive given variations in population, geography, and sample size. Yet the translational trajectory is clear. Future work, they argue, should move beyond descriptive associations toward identifying specific microbial signatures and functional pathways, prioritizing standardized sampling, longitudinal designs, and multi-omics integration with clinical outcomes. Targeted antimicrobials, probiotics, and microbiota-regulating interventions could eventually reshape the oral ecosystem in ways unfavorable to tumor development or supportive of anti-tumor immunity. As a non-invasive, easily collected, and low-cost specimen, saliva may soon join blood and tissue as a routine medium for cancer screening, prognostic evaluation, and personalized medicine, transforming the humble dental checkup into a window on one of medicine’s most formidable diseases.

Subject of Research: The role of oral microbiota dysbiosis in tumorigenesis, cancer prognosis, and early detection

Article Title: Research advances in the correlation between oral microbiota and tumors

Article References: Liu, X., Liu, S., & Guo, Z. (2026). Research advances in the correlation between oral microbiota and tumors. Holistic Integrative Oncology, 5(1), Article 48. https://doi.org/10.1007/s44178-026-00270-z

Image Credits: AI Generated

DOI: 10.1007/s44178-026-00270-z

Keywords: oral microbiota, tumorigenesis, Fusobacterium nucleatum, Porphyromonas gingivalis, oral-gut axis, colorectal cancer, pancreatic cancer, dysbiosis, salivary biomarkers, chronic inflammation, microbiome, cancer screening

Cholecystectomy is a widely performed surgical procedure, primarily indicated for gallstone disease and cholecystitis. Despite its routine nature, the long-term consequences of this operation on intestinal physiology and pathology have remained insufficiently explored. The gallbladder plays a critical role in bile acid metabolism and secretion, which directly influences the composition and activity of the gut microbiota. Tang and colleagues’ study convincingly demonstrates that the loss of the gallbladder disturbs this delicate bile acid–microbiota axis, triggering a cascade of dysbiotic changes that potentiate carcinogenic processes within the colon.

The researchers utilized sophisticated multidimensional approaches, combining murine models with human clinical data analyses to unravel the complex mechanistic pathways involved. They observed that cholecystectomy induced a marked dysbiosis characterized by a decline in beneficial commensal bacteria and an enrichment of opportunistic pathogenic species. This microbial imbalance was accompanied by significant shifts in bile acid profiles, including an increase in secondary bile acids known for their pro-inflammatory and tumor-promoting properties. These biochemical and microbiological aberrations synergistically contributed to chronic intestinal inflammation, a well-established driver of colorectal tumorigenesis.

Delving deeper, the study employed state-of-the-art metagenomic sequencing and metabolomic profiling to chart the precise microbial taxa and metabolites altered post-cholecystectomy. These data unveiled that the expansion of bile-acid–resistant bacteria, coupled with the depletion of short-chain fatty acid-producing microbes, orchestrated a tumorigenic microenvironment within the colon. Short-chain fatty acids, such as butyrate, play a protective role by maintaining epithelial barrier integrity and rectifying immune homeostasis. Their loss thus compromises mucosal defenses, facilitating malignant transformation.

Of particular interest was the finding that secondary bile acids, including deoxycholic acid (DCA), accumulated substantially in the intestines of cholecystectomized mice and patients. DCA has been implicated in DNA damage, oxidative stress, and aberrant activation of oncogenic signaling pathways, such as NF-κB and Wnt/β-catenin, all of which are intimately involved in colorectal cancer pathogenesis. Heightened exposure to these cytotoxic compounds following cholecystectomy effectively creates a pro-carcinogenic niche conducive to the initiation and progression of neoplastic lesions.

The research team further substantiated their observations through histopathological examinations, documenting an increased incidence and severity of precancerous adenomas and malignant tumors in the colons of cholecystectomized animals. Moreover, survival analyses underscored an accelerated disease course and poorer clinical outcomes associated with gut dysbiosis induced by gallbladder removal. This correlation accentuates the clinical importance of preserving or restoring a balanced gut microbiota to mitigate post-surgical colorectal cancer risks.

Importantly, Tang et al. also explored potential interventional strategies to counteract the deleterious microbial and metabolic sequelae of cholecystectomy. They experimented with targeted modulation of the gut microbiota using prebiotics, probiotics, and bile acid sequestrants, which collectively ameliorated dysbiosis and reduced tumor burden in experimental models. These findings herald promising avenues for therapeutic innovation, aiming to attenuate colorectal carcinogenesis through microbiota-centered treatments in patients undergoing gallbladder surgery.

From a molecular perspective, the study elegantly detailed how dysregulated bile acid signaling precipitates epithelial barrier dysfunction through the disruption of tight junction proteins and mucosal immune regulation. This breach facilitates microbial translocation and persistent inflammatory responses, creating a feedback loop that perpetuates oncogenic stimuli. The researchers highlighted specific molecular markers and pathways, such as increased IL-6 and TNF-α expression, and activation of STAT3 signaling, which converge to fuel malignant transformation in the colonic epithelium.

Another intriguing aspect of this study lies in its implications for personalized medicine and cancer prevention. Given the prevalence of cholecystectomy and colorectal cancer worldwide, elucidating this causal link prompts reconsideration of patient monitoring and risk stratification protocols. Surveillance colonoscopy and microbiota profiling might become integral components of post-cholecystectomy care, facilitating early detection of neoplastic changes and enabling timely intervention.

The investigation also raises fundamental questions about the broader systemic impacts of gallbladder removal. Beyond localized colorectal effects, the disturbed bile acid dynamics and altered microbial communities could influence metabolic, immune, and even neurobehavioral health through the gut-liver-brain axis. These multifaceted repercussions underscore the importance of adopting a holistic framework in studying post-cholecystectomy outcomes, integrating microbial ecology with host physiology and oncology.

At the intersection of microbiology, surgery, and oncology, Tang and colleagues’ work exemplifies the power of interdisciplinary research in unraveling complex disease mechanisms. By linking a common surgical procedure with formidable shifts in the gut ecosystem and oncogenic risk, their findings compel a reevaluation of clinical practices and promote innovation in post-operative care strategies that integrate microbiota-targeted therapies.

Moreover, the study exemplifies the emerging paradigm that intestinal microbiota are not passive bystanders but active participants in cancer biology. The capacity of microbial metabolites to influence gene expression, epithelial turnover, and immune surveillance opens new frontiers in designing microbiome-informed diagnostics and therapeutics. The intricate dance between host and microbes following cholecystectomy accentuates the dynamic and plastic nature of disease pathways, dictated by both genetic and environmental factors.

Future research directions prompted by this work are vast and imperative. Longitudinal human studies with expansive cohorts will be necessary to validate the causal relationships and delineate patient subgroups most vulnerable to dysbiosis-induced tumorigenesis. Furthermore, deciphering the temporal dynamics of microbiota and bile acid alterations post-surgery will enhance understanding of critical windows for intervention.

In summary, the novel insights presented by Tang et al. decisively demonstrate that cholecystectomy-induced gut microbiota dysbiosis exacerbates colorectal tumorigenesis through complex metabolic and immunological disruptions. This research not only enhances our comprehension of colorectal cancer pathophysiology but also galvanizes the integration of microbiome science into surgical oncology. The prospect that microbial ecosystem manipulation could become an adjunct modality to lower colorectal cancer risk in patients following gallbladder removal heralds a transformative era in precision medicine.

As colorectal cancer remains a leading cause of cancer mortality globally, unveiling such modifiable factors that potentiate tumor development is especially timely. This study powerfully advocates for heightened awareness of the gut microbiota’s influential role after cholecystectomy and sets the stage for innovative interventions that could mitigate a significant surgical complication. Ultimately, bridging surgical clinical practice with microbiome therapeutics may redefine patient outcomes and elevate standards of care, marking a pivotal advance in oncology.

Subject of Research: The impact of cholecystectomy-related gut microbiota dysbiosis on colorectal tumorigenesis.

Article Title: Cholecystectomy-related gut microbiota dysbiosis exacerbates colorectal tumorigenesis.

Article References:
Tang, B., Li, S., Li, X. et al. Cholecystectomy-related gut microbiota dysbiosis exacerbates colorectal tumorigenesis. Nat Commun 16, 7638 (2025). https://doi.org/10.1038/s41467-025-62956-8

Image Credits: AI Generated