Bacteriome and mycobiome and bacteriome-mycobiome interactions in head and neck squamous cell carcinoma

Unveiling the intratumoral microbiota within cancer landscapes

Recent advances in cancer research have unveiled a significant yet previously underappreciated aspect of oncology: the presence and role of intratumoral microbiota. These microbial residents, encompassing bacteria, fungi, and viruses within tumor tissues, have been found to exert considerable influence on tumor development, progression, and the efficacy of therapeutic interventions. This review aims to synthesize these groundbreaking discoveries, providing an integrated overview of the identification, characterization, and functional roles of intratumoral microbiota in cancer biology. We focus on elucidating the complex interactions between these microorganisms and the tumor microenvironment, highlighting their potential as novel biomarkers and therapeutic targets. The purpose of this review is to offer a comprehensive understanding of the microbial dimension in cancer, paving the way for innovative approaches in cancer diagnosis and treatment.

EnsembleSeq: a workflow towards real-time, rapid, and simultaneous multi-kingdom-amplicon sequencing for holistic and resource-effective microbiome research at scale

Bacterial communities are often concomitantly present with numerous microorganisms in the human body and other natural environments. Amplicon-based microbiome studies have generally paid skewed attention, that too at a rather shallow genus level resolution, to the highly abundant bacteriome, with interest now forking toward the other microorganisms, particularly fungi. Given the generally sparse abundance of other microbes in the total microbiome, simultaneous sequencing of amplicons targeting multiple microbial kingdoms could be possible even with full multiplexing. Guiding studies are currently needed for performing and monitoring multi-kingdom-amplicon sequencing and data capture at scale. Aiming to address these gaps, amplification of full-length bacterial 16S rRNA gene and entire fungal internal-transcribed spacer (ITS) region was performed for human saliva samples (n = 96, including negative and positive controls). Combined amplicon DNA libraries were prepared for nanopore sequencing using a major fraction of 16S molecules and a minor fraction of ITS amplicons. Sequencing was performed in a single run of an R10.4.1 flow cell employing the latest V14 chemistry. An approach for real-time monitoring of the species saturation using dynamic rarefaction was designed as a guiding determinant of optimal run time. Real-time saturation monitoring for both bacterial and fungal species enabled the completion of sequencing within 30 hours, utilizing less than 60% of the total nanopores. Approximately 5 million high quality (HQ) taxonomically assigned reads were generated (~4.2 million bacterial and 0.7 million fungal), providing a wider (beyond bacteriome) snapshot of human oral microbiota at species-level resolution. Among the more than 400 bacterial and 240 fungal species identified in the studied samples, the species of Streptococcus (e.g., Streptococcus mitis and Streptococcus oralis) and Candida (e.g., Candida albicans and Candida tropicalis) were observed to be the dominating microbes in the oral cavity, respectively. This conformed well with the previous reports of the human oral microbiota. EnsembleSeq provides a proof-of-concept toward the identification of both fungal and bacterial species simultaneously in a single fully multiplexed nanopore sequencing run in a time- and resource-effective manner. Details of this workflow, along with the associated codebase, are provided to enable large-scale application for a holistic species-level microbiome study.

IMPORTANCE

Human microbiome is a sum total of a variety of microbial genomes (including bacteria, fungi, protists, viruses, etc.) present in and on the human body. Yet, a majority of amplicon-based microbiome studies have largely remained skewed toward bacteriome as an assumed proxy of the total microbiome, primarily at a shallow genus level. Cost, time, effort, data quality/management, and importantly lack of guiding studies often limit progress in the direction of moving beyond bacteriome. Here, EnsembleSeq presents a proof-of-concept toward concomitantly capturing multiple-kingdoms of microorganisms (bacteriome and mycobiome) in a fully multiplexed (96-sample) single run of long-read amplicon sequencing. In addition, the workflow captures dynamic tracking of species-level saturation in a time- and resource-effective manner.

Oral Mycobiota: A Narrative Review

Numerous studies have proven the important role of the oral microbiota in health and disease. The dysfunctionality of the oral microbiota, known as dysbiosis, is incriminated in dental caries, periodontal disease, oral infectious diseases, oral cancer, and systemic disease. The lesser-known component of the oral microbiota, the mycobiota, is now assiduously investigated. Recent technological developments have helped foster the identification of new fungal species based on genomic research. Next-generation sequencing has expanded our knowledge about the diversity, architecture, and relationships of oral microorganisms within the oral cavity. The mycobiome structure and relationships with the bacteriome have been studied to identify a mycobiotic signature. This review aimed to emphasize the latest knowledge of the oral mycobiome.

Human Mycobiota and Its Role in Cancer Progression, Diagnostics and Therapeutics: A Link Lesser-Known

Although not as well studied as the bacterial component of the human microbiota, the commensal fungi or mycobiota play important roles in maintaining our health by augmenting our immune system. This mycobiota is also associated with various fatal diseases like opportunistic mycoses, and even cancer, with different cancers having respective type-specific mycobiota. The different fungal species which comprise these different intratumoral mycobiota play important roles in cancer progression. The aim of this review paper is to decipher the association between mycobiota and cancer, and shed light on new avenues in cancer diagnosis, and the development of new anti-cancer therapeutics.

Experimental Modeling of Host-Bacterial Interactions in Head and Neck Squamous Cell Carcinoma

The microscopic species colonizing the human body, collectively referred to as the microbiome, play a crucial role in the maintenance of tissue homeostasis, immunity, and the development of disease. There is evidence to suggest associations between alterations in the microbiome and the development of head and neck squamous cell carcinomas (HNSCC). The use of two-dimensional (2D) modeling systems has made significant strides in uncovering the role of microbes in carcinogenesis; however, direct mechanistic links remain in their infancy. Patient-derived three-dimensional (3D) HNSCC organoid and organotypic models have recently been described. Compared to 2D models, 3D organoid culture systems effectively capture the genetic and epigenetic features of parent tissue in a patient-specific manner and may offer a more nuanced understanding of the role of host-microbe responses in carcinogenesis. This review provides a topical literature review assessing the current state of the field investigating the role of the microbiome in HNSCC; including in vivo and in vitro modeling methods that may be used to characterize microbiome-epithelial interactions.

Oral fungal profiling and risk of nasopharyngeal carcinoma: a population-based case-control study

BACKGROUND

Dysbiosis of the oral mycobiome has been linked to some diseases, including cancers. However, the role of oral fungal communities in nasopharyngeal carcinoma (NPC) carcinogenesis has not previously been investigated.

METHODS

We characterized the oral salivary fungal mycobiome in 476 untreated incident NPC patients and 537 population-based controls using fungal internal transcribed spacer (ITS)-2 sequencing. The relationship between oral fungal mycobiome and the risk of NPC was assessed through bioinformatic and biostatistical analyses.

FINDINGS

We found that lower fungal alpha diversity was associated with an increased odds of NPC [lower vs. higher: observed features (adjusted odds ratio [OR] = 5.81, 95% confidence interval [CI] = 3.60-9.38); Simpson diversity (1.53, 1.03-2.29); Shannon diversity (2.03, 1.35-3.04)]. We also observed a significant difference in global fungal community patterns between cases and controls based on Bray-Curtis dissimilarity (P < 0.001). Carriage of oral fungal species, specifically, Saccharomyces cerevisiae, Candida tropicalis, Lodderomyces elongisporus, Candida albicans, and Fusarium poae, was associated with significantly higher odds of NPC, with ORs ranging from 1.56 to 4.66. Individuals with both low fungal and low bacterial alpha diversity had a profoundly elevated risk of NPC.

INTERPRETATION

Our results suggest that dysbiosis in the oral mycobiome, characterized by a loss of fungal community diversity and overgrowth of several fungal organisms, is associated with a substantially increased risk of NPC.

FUNDING

This work was funded by the US National Institutes of Health, the Swedish Research Council, the High-level Talents Research Start-up Project of Fujian Medical University, and the China Scholarship Council.

Fungi and cancer

The microbiome may impact cancer development, progression and treatment responsiveness, but its fungal components remain insufficiently studied in this context. In this review, we highlight accumulating evidence suggesting a possible involvement of commensal and pathogenic fungi in modulation of cancer-related processes. We discuss the mechanisms by which fungi can influence tumour biology, locally by activity exerted within the tumour microenvironment, or remotely through secretion of bioactive metabolites, modulation of host immunity and communications with neighbouring bacterial commensals. We examine prospects of utilising fungi-related molecular signatures in cancer diagnosis, patient stratification and assessment of treatment responsiveness, while highlighting challenges and limitations faced in performing such research. In all, we demonstrate that fungi likely constitute important members of mucosal and tumour-residing microbiomes. Exploration of fungal inter-kingdom interactions with the bacterial microbiome and the host and decoding of their causal impacts on tumour biology may enable their harnessing into cancer diagnosis and treatment.

Metaproteomic Analysis of an Oral Squamous Cell Carcinoma Dataset Suggests Diagnostic Potential of the Mycobiome

Oral squamous cell carcinoma (OSCC) is the most common head and neck malignancy, with an estimated 5-year survival rate of only 40-50%, largely due to late detection and diagnosis. Emerging evidence suggests that the human microbiome may be implicated in OSCC, with oral microbiome studies putatively identifying relevant bacterial species. As the impact of other microbial organisms, such as fungi and viruses, has largely been neglected, a bioinformatic approach utilizing the Trans-Proteomic Pipeline (TPP) and the R statistical programming language was implemented here to investigate not only bacteria, but also viruses and fungi in the context of a publicly available, OSCC, mass spectrometry (MS) dataset. Overall viral, bacterial, and fungal composition was inferred in control and OSCC patient tissue from protein data, with a range of proteins observed to be differentially enriched between healthy and OSCC conditions, of which the fungal protein profile presented as the best potential discriminator of OSCC within the analysed dataset. While the current project sheds new light on the fungal and viral spheres of the oral microbiome in cancer in silico, further research will be required to validate these findings in an experimental setting.

Oral Bacteriome and Mycobiome across Stages of Oral Carcinogenesis

Oral microbial dysbiosis contributes to the development of oral squamous cell carcinoma (OSCC). Numerous studies have focused on variations in the oral bacterial microbiota of patients with OSCC. However, similar studies on fungal microbiota, another integral component of the oral microbiota, are scarce. Moreover, there is an evidence gap regarding the role that microecosystems play in different niches of the oral cavity at different stages of oral carcinogenesis. Here, we catalogued the microbial communities in the human oral cavity by profiling saliva, gingival plaque, and mucosal samples at different stages of oral carcinogenesis. We analyzed the oral bacteriome and mycobiome along the health-premalignancy-carcinoma sequence. Some species, including Prevotella intermedia, Porphyromonas endodontalis, Acremonium exuviarum, and Aspergillus fumigatus, were enriched, whereas others, such as Streptococcus salivarius subsp. salivarius, Scapharca broughtonii, Mortierella echinula, and Morchella septimelata, were depleted in OSCC. These findings suggest that an array of signature species, including bacteria and fungi, are closely associated with oral carcinogenesis. OSCC-associated diversity differences, species distinction, and functional alterations were most remarkable in mucosal samples, not in gingival plaque or saliva samples, suggesting an urgent need to define oral carcinogenesis-associated microbial dysbiosis based on the spatial microbiome. IMPORTANCE Abundant oral microorganisms constitute a complex microecosystem within the oral environment of the host, which plays a critical role in the adjustment of various physiological and pathological states of the oral cavity. In this study, we demonstrated that variations in the "core microbiome" may be used to predict carcinogenesis. In addition, sample data collected from multiple oral sites along the health-premalignancy-carcinoma sequence increase our understanding of the microecosystems of different oral niches and their specific changes during oral carcinogenesis. This work provides insight into the roles of bacteria and fungi in OSCC and may contribute to the development of early diagnostic assays and novel treatments.

Oral microbiota in patients with oropharyngeal cancer with an emphasis on <i>Candida</i> spp

Introduction. Interactions between the 2 microbiota components – bacteria and fungi – are of interest as diagnostic and prognostic markers in selection of treatment tactics for oncological patients.

Aim. To study microbiota of the oral cavity in patients with primary squamous cell carcinoma of the oropharyngeal area before and after surgical intervention to find biomarkers for rational selection of antifungal drugs.

Materials and methods. At the Surgical Department of Head and Neck Tumors of the N. N. Blokhin National Research Center of Oncology, three-component study was performed: investigations of spectrum of Candida spp. isolates, Candida spp. strains’ resistance to antifungals, and oral washes in primary patients before and after surgery. mALDI-Tof microflex LT (Biotyper, Bruker Daltonics, germany) was used for strain identification; Sensititre Yeast ONE, YO10 (Trek Diagnostic System, united kingdom) plates were used for determination of minimal inhibiting concentrations of anti fungals. values of minimal inhibiting concentrations were evaluated based on the European Committee on Antimicrobial Susceptibility Testing (EuCAST) criteria (version 10.0).

Results. four-year observation of patients at the surgical department of head and neck tumors of the N. N. Blokhin National Research Center of Oncology showed that the most common species of Candida is C. albicans (73.5 % of cases). Candida spp. resistance to antifungals was detected only for fluconazole (9.3 % of cases) and micafungin (8.0 % of cases), mostly among C. albicans strains. In 31.8 % of primary patients, oral washes prior to surgery showed growth of Candida spp. (probably, tissue colonization). After surgical intervention, Candida spp. growth was detected in 36.4 % of cases, only 1 of which was diagnosed as invasive mycosis. In 54.5 % of cases before and in 72.7 % of cases after surgery, gram-negative rods were detected. After surgical intervention, percentage of enterobacteria and non-fermenters significantly increased: 59.1 % versus 27.3 % (p <0.05) and 63.6 % versus 27.3 % (p <0.02), respectively. prior to surgery, non-fermenting gram-negative bacteria were represented only by P. aeruginosa; after surgery, the spectrum of non-fermenting gram-negative bacteria became wider but percentage of P. aeruginosa remained high: 71.4 %. ERG11 gene was identified only in 1 strain: C. albicans. FKS1 gene also was identified only in 1 strain: C. inconspicua. virulence factor genes were detected in 57.1 % of strains.

Conclusion. Surgical intervention is associated with changes in bacterial microbiota but not fugal microbiota. presence of virulence factor genes and resistance genes in Candida spp. strains should be considered a biomarker allowing to differentiate between colonization and candida infection and can be used for rational selection of antifungal drugs in prevention and treatment of invasive candidiasis, especially in the absence of criteria for interpretation of measured minimal inhibiting concentrations of antifungals.

The role of the oral microbiome in smoking-related cardiovascular risk: a review of the literature exploring mechanisms and pathways

Cardiovascular disease is a leading cause of morbidity and mortality. Oral health is associated with smoking and cardiovascular outcomes, but there are gaps in knowledge of many mechanisms connecting smoking to cardiovascular risk. Therefore, the aim of this review is to synthesize literature on smoking and the oral microbiome, and smoking and cardiovascular risk/disease, respectively. A secondary aim is to identify common associations between the oral microbiome and cardiovascular risk/disease to smoking, respectively, to identify potential shared oral microbiome-associated mechanisms. We identified several oral bacteria across varying studies that were associated with smoking. Atopobium, Gemella, Megasphaera, Mycoplasma, Porphyromonas, Prevotella, Rothia, Treponema, and Veillonella were increased, while Bergeyella, Haemophilus, Lautropia, and Neisseria were decreased in the oral microbiome of smokers versus non-smokers. Several bacteria that were increased in the oral microbiome of smokers were also positively associated with cardiovascular outcomes including Porphyromonas, Prevotella, Treponema, and Veillonella. We review possible mechanisms that may link the oral microbiome to smoking and cardiovascular risk including inflammation, modulation of amino acids and lipids, and nitric oxide modulation. Our hope is this review will inform future research targeting the microbiome and smoking-related cardiovascular disease so possible microbial targets for cardiovascular risk reduction can be identified.

Mycobiota and C-Type Lectin Receptors in Cancers: Know thy Neighbors

Numerous studies have demonstrated the importance of gut bacteria in the development of malignancy, while relatively little research has been done on gut mycobiota. As a part of the gut microbiome, the percentage of gut mycobiota is negligible compared to gut bacteria. However, the effect of gut fungi on human health and disease is significant. This review systematically summarizes the research progress on mycobiota, especially gut fungi, in patients with head and neck cancer (HNC), esophageal cancer (EC), gastric cancer (GC), colorectal cancer (CRC), hepatocellular carcinoma (HCC), pancreatic cancer, melanoma, breast cancer, and lung carcinoma-induced cachexia. Moreover, we also describe, for the first time in detail, the role of the fungal recognition receptors, C-type lectin receptors (CLRs) (Dectin-1, Dectin-2, Dectin-3, and Mincle) and their downstream effector caspase recruitment domain-containing protein 9 (CARD9), in tumors to provide a reference for further research on intestinal fungi in the diagnosis and treatment of malignant tumors.

Evaluation of Candidiasis in Upper-Aerodigestive Squamous Cell Carcinoma Patients—A Clinico-Mycological Aspect

Candida is a commensal yeast. It can be infective when the host’s defense mechanism is weakened, as in the case of squamous cell carcinoma patients. We aimed to evaluate the prevalence and clinical mycological manifestation of candidiasis in 150 cancer cases comprised of preoperative and post-operative (with or without radiotherapy) upper aerodigestive squamous cell carcinoma. A total of 150 patients suffering from squamous cell carcinoma of the Upper Aero-Digestive Tract (UADT) were divided into preoperative (n = 48), post-operative without radiotherapy (n = 29) and post-operative with radiotherapy (n = 73). Samples were collected using cotton swabs and cultured. Candida species were identified according to color pigmentation on Candida Differential Agar (CDA) plate. The clinico-mycological association of patients was evaluated by the chi-square test, and 98 out of 150 patients showed the presence of various Candida species. The major species isolated was Candida albicans (53%), followed by Candida tropicalis (16%). There was a significant statistical difference between patients who showed mycological associations and patients who did not have any such association (p = 0.0008). The prevalence of oral candidiasis was found to be 65.33% among total cases of upper aero-digestive squamous cell carcinoma. Chronic erythematous cases of candidiasis were mainly seen in preoperative squamous cell carcinoma cases, whereas the acute erythematous type of candidiasis was mainly seen in post-operative cases who received radiotherapy. The clinicomycological assessment can help to correlate the signs and symptoms with the presence of candidiasis in upper aerodigestive squamous cell carcinoma patients. Meticulous testing and examination can help in the early detection of candidiasis. Future studies are needed to develop advance scientific preventive strategies for high-risk cases.

The Mycobiome: Cancer Pathogenesis, Diagnosis, and Therapy

Cancer is among the leading causes of death globally. Despite advances in cancer research, a full understanding of the exact cause has not been established. Recent data have shown that the microbiome has an important relationship with cancer on various levels, including cancer pathogenesis, diagnosis and prognosis, and treatment. Since most studies have focused only on the role of bacteria in this process, in this article we review the role of fungi-another important group of the microbiome, the totality of which is referred to as the "mycobiome"-in the development of cancer and how it can impact responses to anticancer medications. Furthermore, we provide recent evidence that shows how the different microbial communities interact and affect each other at gastrointestinal and non-gastrointestinal sites, including the skin, thereby emphasizing the importance of investigating the microbiome beyond bacteria.

A dysbiotic microbiome promotes head and neck squamous cell carcinoma

Recent studies have reported dysbiotic oral microbiota and tumor-resident bacteria in human head and neck squamous cell carcinoma (HNSCC). We aimed to identify and validate oral microbial signatures in treatment-naïve HNSCC patients compared with healthy control subjects. We confirm earlier reports that the relative abundances of Lactobacillus spp. and Neisseria spp. are elevated and diminished, respectively, in human HNSCC. In parallel, we examined the disease-modifying effects of microbiota in HNSCC, through both antibiotic depletion of microbiota in an induced HNSCC mouse model (4-Nitroquinoline 1-oxide, 4NQO) and reconstitution of tumor-associated microbiota in a germ-free orthotopic mouse model. We demonstrate that depletion of microbiota delays oral tumorigenesis, while microbiota transfer from mice with oral cancer accelerates tumorigenesis. Enrichment of Lactobacillus spp. was also observed in murine HNSCC, and activation of the aryl-hydrocarbon receptor was documented in both murine and human tumors. Together, our findings support the hypothesis that dysbiosis promotes HNSCC development.

The Interaction Between the Microbiome and Tumors

Cancer is a significant global health problem and is characterized by a consistent increase in incidence and mortality rate. Deciphering the etiology and risk factors are essential parts of cancer research. Recently, the altered microbiome has been identified within the tumor microenvironment, tumor tissue, and even nonadjacent environments, which indicates a strong correlation between the microbiome and tumor development. However, the causation and mechanisms of this correlation remain unclear. Herein, we summarized and discussed the interaction between the microbiome and tumor progression. Firstly, the microbiome, which can be located in the tumor microenvironment, inside tumor tissues and in the nonadjacent environment, is different between cancer patients and healthy individuals. Secondly, the tumor can remodel microbial profiles by creating a more beneficial condition for the shifted microbiome. Third, the microbiome can promote tumorigenesis through a direct pathogenic process, including the establishment of an inflammatory environment and its effect on host immunity. The interactions between the microbiome and tumors can promote an understanding of the carcinogenesis and provide novel therapeutic strategies for cancers.

Human papillomavirus infection and tumor microenvironment are associated with the microbiota in patients with oropharyngeal cancers-pilot study

BACKGROUND

Previous microbiome studies of oropharyngeal cancer have shown that there are differences in the oral microbiota between human papillomavirus (HPV)-positive and HPV-negative patients.

METHODS

We collected saliva, normal tissue, and tumor biopsies from 13 patients with oropharyngeal cancer (eight HPV-positive, five HPV-negative). We obtained basic clinical data from each patient. Extracted DNA was 16S rRNA gene sequenced. Analysis was based on HPV status and sample site using univariate, multivariate, and mixed effect regression methods.

RESULTS

Multivariate analysis methods separated samples based on HPV status (Adonis, p < 0.001). Comparison of patients showed that there were significant changes in microbial richness across all sites based on HPV status (linear mixed effects regression, p = 0.0002).

CONCLUSIONS

We found significant differences in overall microbial community and bacterial richness between oropharyngeal patients based on HPV status. Our results suggest that there are significant differences in the microbiome in patients with oropharyngeal cancer based on HPV status.

Mycobiome and Cancer: What Is the Evidence?

Simple Summary

Although comprising a much smaller proportion of the human microbiome, the fungal community has gained much more attention lately due to its multiple and yet undiscovered interactions with the human bacteriome and the host. Head and neck cancer carcinoma, colorectal carcinoma, and pancreatic ductal adenocarcinoma have been associated with dissimilarities in the composition of the mycobiome between cases with cancer and non-cancer subjects. In particular, an abundance of Malassezia has been associated with the onset and progression of colorectal carcinoma and pancreatic adenocarcinoma, while the genera Schizophyllum, a member of the oral mycobiome, is suggested to exhibit anti-cancer potential. The use of multi-omics will further assist in establishing whether alterations in the human mycobiome are causal or a consequence of specific types of cancers.

Abstract

Background: To date, most researchhas focused on the bacterial composition of the human microbiota. In this review, we synopsize recent data on the human mycobiome and cancer, highlighting specific cancer types based on current available evidence, presenting interesting perspectives and limitations of studies and laboratory methodologies. Recent findings: Head and neck cancer carcinoma (HNCC), colorectal carcinoma (CRC) and pancreatic ductal adenocarcinoma (PDA) have been associated with dissimilarities in the composition of mycobiota between cancer cases and non-cancer participants. Overall, fungal dysbiosis with decreased fungal richness and diversity was common in cancer patients; however, a specific mycobiotic signature in HNSCC or CRC has not emerged. Different strains of Candida albicans have been identified among cases with HNCC, whilst Lichtheimia corymbifera, a member of the Mucoraceae family, has been shown to predominate among patients with oral tongue cancer. Virulence factors of Candida spp. include the formation of biofilm and filamentation, and the secretion of toxins and metabolites. CRC patients present a dysregulated ratio of Basidiomycota/Ascomycota. Abundance of Malassezia has been linked to the occurrence and progression of CRC and PDA, particularly in animal models of PDA. Interestingly, Schizophyllum, a component of the oral mycobiome, may exhibit anti-cancer potential. Conclusion: The human mycobiome, per se, along with its interactions with the human bacteriome and the host, may be implicated in the promotion and progression of carcinogenesis. Fungi may be used as diagnostic and prognostic/predictive tools or treatment targets for cancer in the coming years. More large-scale, prospective, multicentric and longitudinal studies with an integrative multi-omics methodology are required to examine the precise contribution of the mycobiome in the etiopathogenesis of cancer, and to delineate whether changes that occur in the mycobiome are causal or consequent of cancer.

Impact of smokeless tobacco-associated bacteriome in oral carcinogenesis

Smokeless tobacco products possess a complex community of microorganisms. The microbial community ferment compounds present in the smokeless tobacco products and convert them into carcinogens like tobacco-associated nitrosamines. However, the potential of smokeless tobacco products associated bacteriome to manipulate systemic inflammation and other signaling pathways involved in the etiology of oral cancer will be a risk factor for oral cancer. Further, damage to oral epithelial cells causes a leaky oral layer that leads to increased infiltration of bacterial components like lipopolysaccharide, flagellin, and toxins, etc. The consumption of smokeless tobacco products can cause damage to the oral layer and dysbiosis of oral microbiota. Hence, the enrichment of harmful microbes due to dysbiosis in the oral cavity can produce high levels of bacterial metabolites and provoke inflammation as well as carcinogenesis. Understanding the complex and dynamic interrelation between the smokeless tobacco-linked bacteriome and host oral microbiome may help to unravel the mechanism of oral carcinogenesis stimulated by smokeless tobacco products. This review provides an insight into smokeless tobacco product-associated bacteriome and their potential in the progression of oral cancer. In the future, this will guide in the evolution of prevention and treatment strategies against smokeless tobacco products-induced oral cancer. Besides, it will assist the government organizations for better management and cessation policy building for the worldwide problem of smokeless tobacco addiction.

New Insights Into the Cancer-Microbiome-Immune Axis: Decrypting a Decade of Discoveries

The past decade has witnessed groundbreaking advances in the field of microbiome research. An area where immense implications of the microbiome have been demonstrated is tumor biology. The microbiome affects tumor initiation and progression through direct effects on the tumor cells and indirectly through manipulation of the immune system. It can also determine response to cancer therapies and predict disease progression and survival. Modulation of the microbiome can be harnessed to potentiate the efficacy of immunotherapies and decrease their toxicity. In this review, we comprehensively dissect recent evidence regarding the interaction of the microbiome and anti-tumor immune machinery and outline the critical questions which need to be addressed as we further explore this dynamic colloquy.

The Role of the Microbiome in Oral Squamous Cell Carcinoma with Insight into the Microbiome-Treatment Axis

Oral squamous cell carcinoma (OSCC) is one of the leading presentations of head and neck cancer (HNC). The first part of this review will describe the highlights of the oral microbiome in health and normal development while demonstrating how both the oral and gut microbiome can map OSCC development, progression, treatment and the potential side effects associated with its management. We then scope the dynamics of the various microorganisms of the oral cavity, including bacteria, mycoplasma, fungi, archaea and viruses, and describe the characteristic roles they may play in OSCC development. We also highlight how the human immunodeficiency viruses (HIV) may impinge on the host microbiome and increase the burden of oral premalignant lesions and OSCC in patients with HIV. Finally, we summarise current insights into the microbiome–treatment axis pertaining to OSCC, and show how the microbiome is affected by radiotherapy, chemotherapy, immunotherapy and also how these therapies are affected by the state of the microbiome, potentially determining the success or failure of some of these treatments.