{"paper_id":"2b74fa95-045d-4e61-9c35-d368f0225e61","body_text":"Gynecological cancers are some of the most common cancers in women, originating from the reproductive organs [ 1 ,  2 ]. These malignancies are the fourth most frequently diagnosed neoplasms in women of childbearing age, accounting for 16% of all neoplasms [ 3 ]. The main types of gynecological cancers are cervical, ovarian, uterine (endometrial cancer and uterine sarcoma), vaginal, and vulvar cancers [ 4 ]. The etiology of gynecological cancers is multifactorial; genetic and epigenetic factors, environmental factors, and infection are the most common risk factors for these malignancies [ 5 ]. Recently, the role of the microbiome in the development of various diseases has been well established [ 6 ,  7 ]. Microbes are involved not only in the onset of gynecologic cancer but also emerge as a result of the physiological disruptions it causes [ 8 ,  9 ]. During dysbiosis, characterized by an imbalance of commensal and pathogenic microorganisms [ 6 ], the reduction and absence of  Lactobacillus  is often observed and replaced by specialized or facultative anaerobic bacteria, compromising the vaginal immune defense [ 10 ]. Decreased estrogen levels are associated with vaginal dysbiosis, characterized by a reduction of regular hydrogen peroxide‐ and lactic acid‐producing  Lactobacillus  species in the vagina and an overgrowth of anaerobic bacteria such as Gardnerella, Mycoplasma, and Prevotella. This shift leads to an increase in vaginal pH above 4.5. Anaerobic bacteria like  \n Gardnerella vaginalis \n  possess virulence factors that allow them to adhere to the host epithelium and form a biofilm [ 11 ]. Dysbiotic bacterial communities release enzymes such as sialidase that compromise the integrity of the mucus barrier and damage the cervicovaginal epithelium, increasing the susceptibility of basal cells to HPV infection. Additionally, certain bacterial toxins can cause DNA damage in host cells, promoting the integration of viral oncogenes into the host genome [ 12 ].\nThe association between viral infections—particularly Human Papillomavirus (HPV) and Human Immunodeficiency Virus (HIV)—and the development of cervical cancer is well established in the literature [ 13 ,  14 ,  15 ].\nAdditionally, chronic infections resulting from PID can contribute to the release of tumor‐promoting factors such as cytokines, chemokines, and reactive oxygen species, fostering genetic and epigenetic changes associated with carcinogenesis [ 16 ].\nFor example, bacterial infections localized in the peritoneum and vaginal infections (such as  \n Neisseria gonorrhoeae \n  or  \n Chlamydia trachomatis \n ) may contribute to the progression and metastasis of ovarian cancer. This may be due to inflammation‐induced oxidative stress, which leads to the accumulation of DNA damage and mutations [ 17 ].\nHowever, the role of bacterial infections in these malignancies has received less attention. Bacteria colonize various human organs and, beyond causing infection‐related conditions, they are implicated in numerous disorders such as obesity, diabetes, fatty liver disease, allergic diseases, atherosclerosis, autoimmune diseases, Alzheimer's disease, and cancer [ 18 ,  19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  25 ,  26 ]. The association between bacterial infections and cancer development is complex and not yet fully understood. However, genetic susceptibility and inflammation appear to be key mediators in this association. In this study, we aim to present new findings on the role of different bacterial infections in various types of gynecological cancers by reviewing recent literature.\n\nIn this review, data on the role of bacterial infections in the development of gynecological cancers were collected from databases including PubMed, Scopus, and Google Scholar. Published manuscripts were searched using keywords such as bacterial infections, gynecological cancers, and microbiome in reproductive organs. All English‐language articles were screened and independently read by two authors. An overview of the literature search strategy, including inclusion/exclusion criteria and results, is provided in Figure  S1 .\n\nPromotion and progression of cancer is a complex multistage process, which is accompanied by genetic alterations. Genetic alterations can be induced by various internal and external agents. The role of bacterial infection as an external factor has been established in several cancers [ 24 ,  25 ,  26 ,  27 ]. For instance, it has been known that  \n Helicobacter pylori \n  ( \n H. pylori \n ) infection could be associated with gastric cancer promotion [ 26 ,  28 ]. World Health Organization (WHO) defined  \n H. pylori \n  as class I carcinogens [ 28 ]. The other well‐known bacterial infections are chronic  \n Salmonella typhi \n  ( \n S. typhi \n ) infections, which are associated with gallbladder cancer, and  \n Salmonella enteritidis \n  associated with colon cancers [ 29 ]. Other bacteria related to cancer promotion in different organs are listed in Table  1 . Investigations in germ‐free and antibiotic‐treated animals showed that bacteria can promote cancer in different experimental systems such as colon and liver cancers [ 30 ,  31 ]. The mechanisms by which bacteria can promote development of cancers are not fully addressed. However, several likely mechanisms have been suggested, which are categorized into bacterial cell‐surface components, bacterial toxins, and effector proteins. These components are derived from chronic inflammation, which may change normal physiological processes and result in genomic instability and promotion of cancer development [ 24 ,  25 ,  32 ]. For example, it has been shown that the high level of adhesion A (fadA) of  \n Fusobacterium nucleatum \n  is linked to overexpression of Wnt signaling pathway genes, which are involved in inflammation and tumorgenicity [ 24 ,  33 ]. In addition, CagL of  \n H. pylori \n  increases gastric secretion and is linked to hypergastrinemia, which may lead to gastric cancer [ 34 ]. CagL is found in  \n H. pylori \n  strains that carry the type IV secretion system (T4SS), which is encoded by the Cag pathogenicity island and recognized as the main virulence factor of this bacterium. CagL is located at the tip of the T4SS, where it acts as a specialized adhesin that binds and activates the α5β1 integrin receptor on gastric epithelial cells through its arginine‐glycine‐aspartate (RGD) motif, thereby promoting the injection of the bacterial oncoprotein CagA into host cells [ 35 ,  36 ]. The interaction between the  \n H. pylori \n  T4SS and host integrin α5β1 can trigger the activation of NF‐κB signaling and induce the release of key pro‐inflammatory cytokines. This can lead to more severe clinical outcomes, including gastric carcinogenesis [ 37 ]. Recent studies have also shown that CagL can stimulate the expression of ADP‐ribosyltransferase, NAD‐glycohydrolase, and auto‐ADP‐ribosylation activities. This highlights its potential as a candidate for  \n H. pylori \n  vaccine development [ 38 ].\nDifferent bacterial infections related to cancer promotion in different gynecological organs.\nAnother example is the blood group antigen‐binding adhesin BabA of  \n H. pylori \n , which is related to high levels of inflammatory cytokines and interleukins such as CCL5 and IL‐8. In addition, bacterial protein may increase cancer‐related genes such as CDX2 and MUC2 involved in colorectal cancer [ 39 ]. Furthermore, lipopolysaccharides (LPS), a bacterial cell‐surface component, activate host Toll‐like receptor‐4 (TLR‐4), which is related to several inflammatory pathways. The association of TLR4 activation and cancer has been identified in a mice model of colorectal cancer. It has been shown that TLR4 is overexpressed in colorectal patients [ 24 ,  40 ].\nSeveral bacterial products such as toxins and metabolites cause DNA damage and dysregulation of key factors, which are related to the host cell cycle and cell division regulation. For instance, cytolethal distending toxin (CDT), which is produced by numerous Gram‐negative bacteria such as  \n S. typhi \n ,  \n E. coli \n , and  \n Shigella  dysenteriae , induces double stranded DNA (ds DNA) breaks in the host genome. The role of the toxin is studied well in gallbladder cancer [ 41 ]. CDT also promotes mitogen‐activated protein kinase (MAPK) activity, which is related to oncogenic pathways [ 42 ]. In addition to CDT, colibactin toxin is secreted by group B2  \n E. coli \n  strains harboring the polyketide synthetase (pks) island, induces ds DNA breaks in the host genome and leads to tumorigenesis in the host cells [ 43 ]. Furthermore, several bacterial toxins induce tumorigenesis by increasing and decreasing cell proliferative and cell death factors. CagA of  \n H. pylori \n  activates c‐Met receptor of epithelial cells, which is a proliferative factor of the cells. In addition, CagA can induce tumorigenesis of gastric epithelial cells via interaction with different cancer‐related pathways including MEK, ERK, and β‐catenin pathways [ 29 ,  44 ,  45 ]. Enteric  Salmonella  effector AvrA intervenes with different colon cell signaling pathways, changes immune response, apoptosis, and cell proliferation [ 46 ]. Overall, pathogenic bacteria manipulate the host cells' niche through different mechanisms, and the identification of these mechanisms can be useful in combating them.\n\nWomen's reproductive organs have a dynamic and relative microbial balance. Gynecologic cancers originate in the reproductive organs of women, commonly affecting the cervix, endometrium, and ovaries, while cancers of the vagina and vulva are less frequent. Alterations in the gut and vaginal microbiome composition influence the immune and metabolic signaling of host cells, leading to chronic inflammation, angiogenesis, cellular proliferation, genome instability, breaches in the epithelial barrier, and metabolic dysregulation that may trigger the progression of gynecologic cancers. An imbalance in the microbiome, as well as, gynecological cancers. The association of different types of gynecological cancers including cervical, ovarian, uterine (endometrial cancer and uterine sarcoma), vaginal, and vulvar cancers with different bacterial infections has been investigated in several researches which are discussed in the following sections. The most important bacteria associated with different types of gynecological cancers and the related mechanisms are summarized in Table  2  and Figure  1 , respectively.\nThe different bacterial infections associated with gynecological cancers development.\nThe different bacteria and their induced mechanisms associated with various gynecological organs.\n\nOvarian cancer is one of the most common deadly of gynecological cancers and risk of this cancer is about 1 in 78 women. According to American cancer society's statistics center, 22 530 new cases were estimated, which were 2.5% of all novel cancer cases, and 13 980 mortalities were estimated that 5% of all cancer deaths in 2019 ( www.cancer.org ). In addition, ovarian cancer is fifth causes of cancer‐related mortality among women and most commonly occurs in 63 years old or older and white women ( www.cancer.org ). Identified risk factors associated with this cancer are included hereditary factors such as Lynch syndrome (hereditary nonpolyposis colon cancer), alteration or mutation of  BRCA1  and  BRCA2  genes (tumor suppressor genes) and family history of either breast or ovarian cancer [ 47 ,  48 ]. The risk of ovarian cancer is assessed to be 40%–50% and 10%–25% for  BRCA1  and  BRCA2  mutation‐carriers, respectively [ 49 ]. The BARD protein interacts with p53 protein to regulate cell division and promote apoptosis or control cell death [ 50 ].\nIn addition, infertility, late menopause, hormone replacement therapy with androgens and estrogen, pelvic inflammatory disease (PID), endometriosis, polycystic ovary syndrome, lifestyle (obesity), and geography can be associated with an increased risk of ovarian cancer [ 51 ]. A study showed that breastfeeding and pregnancy frequency decrease ovarian cancer risk [ 52 ]. Several studies have been shown that bacterial infections are another important risk factor for the malignancy.\nChlamydia trachomatis \n  is one of the most prevalent sexually transmitted microorganisms in the world [ 53 ]. Initial infection with  \n C. trachomatis \n  intracellular exhibits an asymptomatic period and may persist for years that reveals failure of the host immune responses [ 54 ]. The innate immune system initiates by the binding receptors named pattern of recognitions (PRRs) such as the nucleotide‐binding oligomerization domain proteins (NODs) and the Toll‐like receptors (TLRs) to pathogen‐associated molecular patterns (PAMPs), activating NF‐ĸB that NF‐ĸB attaches to nuclear DNA thus producing pro‐inflammatory cytokines [ 55 ]. These pro‐inflammatory cytokines are included IL‐6, IL‐8, IL‐10, IL‐12, and IFN‐γ. Macrophages and neutrophils that induce inflammatory responses, stimulate tissue damage and inhibit host cell apoptosis that can help ovarian carcinogenesis subsequent  Chlamydia  infections [ 52 ,  56 ]. It has been shown that 80% of OC cases were positive for  Chlamydia  infections [ 57 ]. HSP60 is synthesized as an immune protein during infection with  Chlamydia  that contains common antigenic epitopes and can lead to stimulate immune responses [ 56 ]. Binging of TLRs to HSP60 induces production of adhesion factors and the inflammatory chronic response [ 58 ]. HSP60 by inducing a series of reactions, by activation of caspase cascade, could inhibit apoptosis [ 59 ]. Tsai et al. have demonstrated that overexpression of HSP60 promotes tumorigenesis and metastasis [ 60 ]. The elevated levels of serum IgG antibody against HSP60 were found in ovarian cancer patients that is recognized as risk factor for the malignancy [ 61 ].  \n C. trachomatis \n  can stimulate the production of reactive oxygen species (ROS) through the Mitochondrial Nod‐like Family Member NLRX1. ROS production is typically a cellular defense mechanism against invading microorganisms. However,  \n C. trachomatis \n  can override cellular defenses and utilize ROS to enhance its own growth by activating caspase‐1. The resulting elevated levels of ROS can cause to double‐stranded DNA damages in the infected cell. Moreover,  \n C. trachomatis \n  can diminish the DNA damage response (DDR) through inhibition of DDR proteins pATM and 53BP1 [ 62 ,  63 ]. In spite of the DNA damage, cells infected with Chlamydia continue to proliferate due to the activation of MAPK signaling and the expression of cyclin E [ 63 ]. Ultimately,  \n C. trachomatis  can  trigger the proteasomal degradation of P53 through interaction with the phosphorylated ubiquitin ligase Murine Double Minute 2 (MDM2), resulting in inhibition of apoptosis. Combined, these mechanisms enhance bacterial survival, but they can also potentially lead to genomic instability, disruption of the cell cycle, and inhibition of apoptosis, all of which are key characteristics of cancer [ 63 ,  64 ,  65 ].\nMycoplasma genitalium \n  is another sexually transmitted bacterium that causes urethritis, pelvic inflammatory disease (PID), cervicitis, vaginitis and infertility in females [ 66 ]. Banerjee et al. showed that 74% of the malignant ovarian cancer samples contained  \n M. genitalium \n  [ 67 ]. The another study was detected increased levels of serum  \n M. genitalium \n  IgG antibodies in ovarian cancer patients in comparison to controls [ 57 ].  \n M. genitalium \n  produces toxins, which can lead to swelling of the fallopian tube epithelium cells that are the origin of ovarian cancer [ 68 ]. A study by Zhou et al. using 16S rRNA high‐throughput sequencing methods and normal distal fallopian tube transcriptome‐sequencing (RNA‐seq) analyses of ovarian cancer and tissues demonstrated that  Proteobacteria ,  Firmicutes , and  \n Acinetobacter lwoffii \n  are associated with ovarian cancer [ 69 ].\n\nUterine cancer is the most prevalent type of gynecological cancer and the fourth most prevalent cancer with about 61 880 new cases (7% of all cancer cases) with 12 160 deaths (4% of all tumor deaths) among the US women in 2019 ( www.cancer.org ). This cancer is more common in women between the ages of 55 and 74 and white women (www.  cancer.org ).\nThe 80% of the causative agents of endometrial cancer are associated with the environmental and host factors including increasing age, obesity, diabetes mellitus, late menopause, having no children, long‐term use of tamoxifen and excessive use of estrogen [ 70 ]. The remaining 20% of cases are related to Lynch syndrome, Cowden syndrome and family history of breast, ovarian and/or endometrial cancer [ 71 ]. Bacterial infections are also involved in the malignancy. The pathogenic bacteria could cause to boost via the vaginal or cervix into the upper genital tract and lead to PID, the uterus and endothelial dysfunction, thus promoting carcinogenesis [ 72 ]. Recent discoveries have challenged the traditional view of the uterus as a completely sterile environment [ 73 ]. New research suggests that the endometrium actually hosts a distinct community of microorganisms that can influence how tumors interact with surrounding tissues and affect cancer cell signaling [ 74 ]. In studies involving patients with endometrial cancer, researchers have consistently found that certain groups of bacteria are particularly prevalent. These include Bacteroidetes, such as  Bacteroides ,  Porphyromonas ,  Flavobacterium , and  Prevotella ; Actinobacteria, with  Atopobium  being a notable member; Firmicutes, which includes  Anaerococcus ,  Dialister ,  Peptoniphilus ; and  Proteobacteria , represented by  Pseudomonas  and  Acidovorax . This highlights the diverse microbial life present in the endometrium and its potential impact on health [ 75 ,  76 ,  77 ].\n\nThe carcinoma of the cervix is one of the most prevalent tumors in women. The malignancy is the fourth cause of cancer‐related deaths in women worldwide [ 78 ]. Squamous cell carcinoma and adenocarcinoma are the most important kinds of cervical cancers [ 79 ]. Continuous infection with HR‐HPV is an important factor in the promotion of cervical cancer [ 80 ]. Besides that, several risk factors such as smoking, multiple sexual partners, marrying before age 18 years old, multiple childbirths, and bacterial infections have been known for the malignancy [ 81 ].\nThere is a microbial balance in the vagina. The most common microorganisms in the intact vagina are  Lactobacillus  spp., which are also involved in the defense of the reproductive system. The disruption in the balance of vaginal flora during physiological conditions results in numerous gynecological diseases, such as colitis, high‐grade cervical intraepithelial neoplasia (CIN) and cervical cancer [ 82 ]. Reduction of the  Lactobacillus  spp. population results in overgrowing of anaerobic infections [ 83 ]. Up to now, the link among vaginal bacteria and cervical cancer has not been identified; but several researches have reported that the frequency of various bacteria such as  \n Gardnerella vaginalis \n ,  \n Prevotella bivia \n ,  \n Mycoplasma genitalium \n ,  \n Staphylococcus epidermidis \n ,  Enterococcus  spp.,  \n Escherichia coli \n ,  Fusobacterium  spp., and  Bacteroides  spp. is different in the cancerous women in comparison to healthy women [ 84 ,  85 ,  86 ]. These bacteria promote tumorogenesis through the activation of host immunity and production of various metabolites. Anaerobe bacteria release high levels of polyamines and organic acids including acetic and succinic acids, which are toxic to the cells. The evaluated levels of nitrosamines lead to DNA breakdown and change cytokine releasing that influences the immune responses to the HPV. So, the anaerobic bacteria promote the risk of HPV infections and cervical cancer [ 87 ,  88 ]. Also, the bacteria release numerous immunomodulatory factors including proteases, sialidases, and succinate [ 89 ]. In addition, inflammatory‐inducing substances such as lipoteichoic acid, peptidoglycans and LPS can result in the release of proinflammatory cytokines such as IL‐6 and IL‐8 [ 88 ]. It has been reported that the cytokines promote angiogenesis and carcinogenesis of solid cancers [ 90 ]. In addition, the vaginal bacteria activate TGFβ through activation of TLR. TGFβ promotes the expression of integrins and progresses the invasion of solid tumors [ 91 ].\n\nVulvar cancer is a rare type of cancer that accounts for approximately 5% of gynecological cancer. Vulvar cancer is raised from the tissues of the vulva and usually affects postmenopausal women. There were 6170 new cases of vulvar cancer (0.3% of all new cancer cases), with 1280 deaths a year (0.2% of all cancer deaths) in the United States in 2019. This cancer is often observed in women after the age of 45 and from lower social classes [ 92 ].\nThe increasing age, smoking cigarettes, having chronic skin conditions and inflammation, history of vulvar or cervical intraepithelial neoplasia, weakened immune system (HIV infection) and Human papilloma virus (HPV) infection increase the risks of vulvar cancer [ 93 ]. As with the other gynecological cancers, bacterial infections are involved in the malignancy. Boutas et al. [ 94 ] reported that  \n Bacteroides fragilis \n  ( \n B. fragilis \n ) was found in a 78‐year‐old woman with vulvar cancer.  \n B. fragilis \n  can promote carcinogenesis via production of fragilysin and metalloproteinase, which lead to the stimulation of synthesis of cyclin D and c‐Myc proteins (as transcription factors) by releasing β‐catenin [ 95 ]. In addition, fragilysin triggers activation of STAT3 transcription factors and NF‐κB that activates the synthesis of proinflammatory cytokines with oncogenic effects [ 95 ,  96 ].\nIn addition, there is an association between  \n C. trachomatis \n  infection and vulvar cancer [ 97 ]. In addition,  \n C. trachomatis \n  antigen was detected in 20% of patients with vulvar cancer, and antibodies of IgM and IgG  Chlamydia  were found in 13.3% and 50% of these patients [ 98 ].\n\nVaginal cancer is one of the rarest of gynecological cancers and is only 2% of all gynecological cancers with about 1 of every 1100 women. It was estimated that 5170 new cases and 1430 deaths in the United States in 2019 ( www.cancer.org ). The risk of vaginal cancer is associated with women 70 years old or older in more than half of the cases, prenatal exposure to diethylstilbestrol, smoking, a previous history of cervical cancer, and viral infections such as human papillomavirus (HPV 16 and HPV 18) and human immunodeficiency virus (HIV) [ 99 ]. In addition, bacterial infections may be involved in the pathogenesis of vaginal cancer. The most common causes of bacteria in vaginal cancer are  Lactobacillus  spp. including  \n L. iners \n ,  \n L. crispatus \n ,  \n L. jensenii \n , and  \n L. gasseri \n , with  \n L.  iners , and  \n L. crispatus \n  being the dominant species among them [ 100 ].  Lactobacillus  spp. through the induction of cytokine production including TNF‐α, IFN‐γ, IL‐12, IL‐18, Nod2, and TLR2 activate innate immune responses to protect the genital tract host [ 101 ]. On the other hand,  Lactobacillus  spp. through lactic acid production provide a pH > 4.5, which prevents the invasion of pathogenic bacteria in the vaginal environment [ 102 ].  Mycoplasma spp . is a commensal bacterium of humans that switch into a pathogenic state by altered host immunity or microbial environment, causing vaginal cancer [ 103 ].\nAlteration of the vaginal flora, a decrease in the proportion of  Lactobacillus  spp., can lead to increase incidence of bacterial vaginosis such as  \n Gardnerella vaginalis \n ,  \n Atopobium vaginae \n ,  Mycoplasma  spp.,  Clostridiales ,  Prevotella  spp., and  Megasphaera  spp. [ 104 ]. The vaginal  Lactobacillus  spp. seem to be protective, and a disruption of them can cause reduced immune protection and damage the epithelial lining of reproductive tissues, as well as, replacement of bacterial vaginosis, thereby promoting carcinogenesis [ 105 ].\nThe important known bacteria, which promote inflammation in vagina are  \n A. vaginae \n ,  \n G. vaginalis \n , and  \n Mycoplasma hominis \n .  \n A. vaginae \n  induces pro‐inflammatory cytokines IL‐6, IL‐8, and the antimicrobial peptide b‐defensin 4 via the binding TLR1, −2 and −6 to NF‐kB signaling from vaginal epithelial cells [ 106 ].  \n G. vaginalis \n  induces IL‐6 and IL‐8 and  \n Mycoplasma hominis \n  induces TNFα, which are involved in inflammation and may be in cancer development [ 107 ].\n\nGynecological cancers are one of the most common cancers in women that affect their reproductive organs. The role of bacterial infection as an external factor has been established in several cancers, as well as gynecological cancers. However, the mechanisms of carcinogenesis of bacteria are unclear. Women's reproductive organs have a dynamic and relative microbial balance. The disruption in the balance of the microbiome could result in numerous gynecological diseases and gynecological cancers. Among the different bacterial infections, infections caused by  Chlamydia ,  Mycoplasma , and  Bacteriodes  species are important infections associated with the malignancies. Evaluation of the microbiome in the reproductive organs of gynecological cancer patients and studies on the prevention and control of the infections in the patients could be useful in verifying the pathogenesis of the diseases and also the identification of suitable therapeutic strategies.\n\nRobab Azargun:  methodology, writing – original draft.  Maryam Azargoon:  methodology, writing – review and editing.  Zahra Asefy:  investigation, writing – review and editing.  Mina Yekani:  software, writing – review and editing.  Vahideh Tarhriz:  investigation, writing – review and editing.  Fatemeh Yeganeh:  methodology, writing – original draft.  Mohammad Yousef Memar:  supervision, writing – review and editing.  Shirin Eyvazi:  validation, writing – review and editing.\n\nThe authors have nothing to report.\n\nThe authors have nothing to report.\n\nThe authors declare no conflicts of interest.\n\nFigure S1:  An overview of the literature search strategy.","source_license":"CC-BY-4.0","license_restricted":false}