Gut Microbes in Gynecologic Cancers: Causes or Biomarkers and Therapeutic Potential

Gut and oral microbiota in gynecological cancers: interaction, mechanism, and therapeutic value

Gynecologic cancers develop from the female reproductive organs. Microbial dysbiosis in the gut and oral cavity can communicate with each other through various ways, leading to mucosal destruction, inflammatory response, genomic instability, and ultimately inducing cancer and worsening. Here, we introduce the mechanisms of interactions between gut and oral microbiota and their changes in the development of gynecologic tumors. In addition, new therapeutic approaches based on microbiota modulation are discussed.

The Gut Microbiome in Aging and Ovarian Cancer

The gut microbiome changes with age and affects regions beyond the gut, including the ovarian cancer tumor microenvironment. In this review summarizing the literature on the gut microbiome in ovarian cancer and in aging, we note trends in the microbiota composition common to both phenomena and trends that are distinctly opposite. Both ovarian cancer and aging are characterized by an increase in proinflammatory bacterial species, particularly those belonging to phylum Proteobacteria and genus Escherichia, and a decrease in short chain fatty acid producers, particularly those in Clostridium cluster XIVa (family Lachnospiraceae) and the Actinobacteria genus Bifidobacterium. However, while beneficial bacteria from family Porphyromonadaceae and genus Akkermansia tend to increase with normal, healthy aging, these bacteria tend to decrease in ovarian cancer, similar to what is observed in obesity or unhealthy aging. We also note a lack in the current literature of research demonstrating causal relationships between the gut microbiome and ovarian cancer outcomes and research on the gut microbiome in ovarian cancer in the context of aging, both of which could lead to improvements to ovarian cancer diagnosis and treatment.

Fusobacterium nucleatum: An Overview of Evidence, Demi-Decadal Trends, and Its Role in Adverse Pregnancy Outcomes and Various Gynecological Diseases, including Cancers

Gynecological and obstetric infectious diseases are crucial to women's health. There is growing evidence that links the presence of Fusobacterium nucleatum (F. nucleatum), an anaerobic oral commensal and potential periodontal pathogen, to the development and progression of various human diseases, including cancers. While the role of this opportunistic oral pathogen has been extensively studied in colorectal cancer in recent years, research on its epidemiological evidence and mechanistic link to gynecological diseases (GDs) is still ongoing. Thus, the present review, which is the first of its kind, aims to undertake a comprehensive and critical reappraisal of F. nucleatum, including the genetics and mechanistic role in promoting adverse pregnancy outcomes (APOs) and various GDs, including cancers. Additionally, this review discusses new conceptual advances that link the immunomodulatory role of F. nucleatum to the development and progression of breast, ovarian, endometrial, and cervical carcinomas through the activation of various direct and indirect signaling pathways. However, further studies are needed to explore and elucidate the highly dynamic process of host-F. nucleatum interactions and discover new pathways, which will pave the way for the development of better preventive and therapeutic strategies against this pathobiont.

Associations between gut microbiota and gynecological cancers: A bi-directional two-sample Mendelian randomization study

Growing evidence has suggested that gut microbiota is associated with gynecologic cancers. However, whether there is a causal relationship between these associations remains to be determined. A two-sample Mendelian randomization (MR) evaluation was carried out to investigate the mechanism associating gut microbiota and 3 prevalent gynecological cancers, ovarian cancer (OC), endometrial cancer, and cervical cancer as well as their subtypes in individuals of European ancestry. The Genome-wide association studies statistics, which are publically accessible, were used. Eligible instrumental single nucleotide polymorphisms that were significantly related to the gut microbiota were selected. Multiple MR analysis approaches were carried out, including inverse variance weighted, MR-Egger, Weighted Median methods, and a range of sensitivity analyses. Lastly, we undertook a reverse MR analysis to evaluate the potential of reverse causality. We sifted through 196 bacterial taxa and identified 33 suggestive causal relationships between genetic liability in the gut microbiota and gynecological cancers. We found that 11 of these genera could be pathogenic risk factors for gynecological cancers, while 19 could lessen the risk of cancer. In the other direction, gynecological cancers altered gut microbiota composition. Our MR analysis revealed that the gut microbiota was causally associated with OC, endometrial cancer, and cervical cancer. This may assist in providing new insights for further mechanistic and clinical studies of microbiota-mediated gynecological cancer.

Gynecological Cancers and Microbiota Dynamics: Insights into Pathogenesis and Therapy

In recent years, the relationship between the microbiota and various aspects of health has become a focal point of scientific investigation. Although the most studied microbiota concern the gastrointestinal tract, recently, the interest has also been extended to other body districts. Female genital tract dysbiosis and its possible impact on pathologies such as endometriosis, polycystic ovary syndrome (PCOS), pelvic inflammatory disease (PID), and gynecological cancers have been unveiled. The incursion of pathogenic microbes alters the ecological equilibrium of the vagina, triggering inflammation and compromising immune defense, potentially fostering an environment conducive to cancer development. The most common types of gynecological cancer include cervical, endometrial, and ovarian cancer, which occur in women of any age but especially in postmenopausal women. Several studies highlighted that a low presence of lactobacilli at the vaginal level, and consequently, in related areas (such as the endometrium and ovary), correlates with a higher risk of gynecological pathology and likely contributes to increased incidence and worse prognosis of gynecological cancers. The complex interplay between microbial communities and the development, progression, and treatment of gynecologic malignancies is a burgeoning field not yet fully understood. The intricate crosstalk between the gut microbiota and systemic inflammation introduces a new dimension to our understanding of gynecologic cancers. The objective of this review is to focus attention on the association between vaginal microbiota and gynecological malignancies and provide detailed knowledge for future diagnostic and therapeutic strategies.

Human Papillomavirus Infections and the Role Played by Cervical and Cervico-Vaginal Microbiota-Evidence from Next-Generation Sequencing Studies

This comprehensive review encompasses studies examining changes in the cervical and cervico-vaginal microbiota (CM and CVM) in relation to human papillomavirus (HPV) using next-generation sequencing (NGS) technology. HPV infection remains a prominent global health concern, with a spectrum of manifestations, from benign lesions to life-threatening cervical cancers. The CM and CVM, a unique collection of microorganisms inhabiting the cervix/vagina, has emerged as a critical player in cervical health. Recent research has indicated that disruptions in the CM and CVM, characterized by a decrease in Lactobacillus and the overgrowth of other bacteria, might increase the risk of HPV persistence and the progression of cervical abnormalities. This alteration in the CM or CVM has been linked to a higher likelihood of HPV infection and cervical dysplasia. NGS technology has revolutionized the study of the cervical microbiome, providing insights into microbial diversity, dynamics, and taxonomic classifications. Bacterial 16S rRNA gene sequencing, has proven invaluable in characterizing the cervical microbiome, shedding light on its role in HPV infections and paving the way for more tailored strategies to combat cervical diseases. NGS-based studies offer personalized insights into an individual's cervical microbiome. This knowledge holds promise for the development of novel diagnostic tools, targeted therapies, and preventive interventions for cervix-related conditions, including cervical cancer.

Gut Microbiome Dysbiosis in Patients with Endometrial Cancer vs. Healthy Controls Based on 16S rRNA Gene Sequencing

Metabolic diseases like obesity, diabetes, and hypertension are considered major risk factors associated with endometrial cancer. Considering that an imbalance in the gut microbiome may lead to metabolic alterations, we hypothesized that alteration in the gut microbioma might be an indirect factor in the development of endometrial cancer. Our aim was to profile the gut microbiota of patients with endometrial cancer compared with healthy controls in this study. Thus, we used 16S rRNA high-throughput gene sequencing on the Illumina NovaSeq platform to profile microbial communities. Fecal samples were collected from 33 endometrial cancer patients (EC group) and 32 healthy controls (N group) between February 2021 and July 2021. The total numbers of operational taxonomic units (OTUs) in the N and EC groups were 28,537 and 18,465, respectively, while the number of OTUs shared by the two groups was 4771. This study was the first to report that the alpha diversity of the gut microbiota was significantly reduced in endometrial cancer patients vs. healthy controls. Also, there was a significant difference in the distribution of microbiome between the two groups: the abundance of Firmicutes, Clostridia, Clostridiales, Ruminococcaceae, Faecalibacterium, and Gemmiger_formicis decreased, while that of Proteobacteria, Gammaproteobacteria, Enterobacteriales, Enterobacteriaceae and Shigella increased significantly in the EC group vs. healthy controls (all p < 0.05). The predominant intestinal microbiota of the endometrial cancer patients was Proteobacteria, Gammaproteobacteria, Enterobacteriales, Enterobacteriaceae, and Shigella. These results imply that adjusting the composition of the gut microbiota and maintaining microbiota homeostasis may be an effective strategy for preventing and treating endometrial cancer.

Female reproductive tract-organ axes

The female reproductive tract (FRT) and remote/versatile organs in the body share bidirectional communication. In this review, we discuss the framework of the "FRT-organ axes." Each axis, namely, the vagina-gut axis, uterus-gut axis, ovary-gut axis, vagina-bladder axis, vagina-oral axis, uterus-oral axis, vagina-brain axis, uterus-brain axis, and vagina-joint axis, is comprehensively discussed separately. Each axis could be involved in the pathogenesis of not only gynecological diseases but also diseases occurring apart from the FRT. Although the microbiota is clearly a key player in the FRT-organ axes, more quantitative insight into the homeostasis of the microbiota could be provided by host function measurements rather than current microbe-centric approaches. Therefore, investigation of the FRT-organ axes would provide us with a multicentric approach, including immune, neural, endocrine, and metabolic aspects, for understanding the homeostatic mechanism of women's bodies. The framework of the FRT-organ axes could also provide insights into finding new therapeutic approaches to maintain women's health.

Association between diabetes and cancer. Current mechanistic insights into the association and future challenges

Compelling pieces of epidemiological, clinical, and experimental research have demonstrated that Diabetes mellitus (DM) is a major risk factor associated with increased cancer incidence and mortality in many human neoplasms. In the pathophysiology context of DM, many of the main classical actors are relevant elements that can fuel the different steps of the carcinogenesis process. Hyperglycemia, hyperinsulinemia, metabolic inflammation, and dyslipidemia are among the classic contributors to this association. Furthermore, new emerging actors have received particular attention in the last few years, and compelling data support that the microbiome, the epigenetic changes, the reticulum endoplasmic stress, and the increased glycolytic influx also play important roles in promoting the development of many cancer types. The arsenal of glucose-lowering therapeutic agents used for treating diabetes is wide and diverse, and a growing body of data raised during the last two decades has tried to clarify the contribution of therapeutic agents to this association. However, this research area remains controversial, because some anti-diabetic drugs are now considered as either promotors or protecting elements. In the present review, we intend to highlight the compelling epidemiological shreds of evidence that support this association, as well as the mechanistic contributions of many of these potential pathological mechanisms, some controversial points as well as future challenges.