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Fusobacterium nucleatum: a novel immune modulator in breast cancer?

Published online by Cambridge University Press:  03 April 2023

Alexa Little
Affiliation:
School of Pharmacy, Queen's University Belfast, Belfast, Northern Ireland, UK
Mark Tangney
Affiliation:
Cancer Research, University College Cork, Cork, Ireland APC Microbiome Ireland, University College Cork, Cork, Ireland
Michael M. Tunney
Affiliation:
School of Pharmacy, Queen's University Belfast, Belfast, Northern Ireland, UK
Niamh E. Buckley*
Affiliation:
School of Pharmacy, Queen's University Belfast, Belfast, Northern Ireland, UK
*
Corresponding author: Niamh E Buckley, E-mail: [email protected]
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Abstract

Breast cancer was the most commonly diagnosed cancer worldwide in 2020. Greater understanding of the factors which promote tumour progression, metastatic development and therapeutic resistance is needed. In recent years, a distinct microbiome has been detected in the breast, a site previously thought to be sterile. Here, we review the clinical and molecular relevance of the oral anaerobic bacterium Fusobacterium nucleatum in breast cancer. F. nucleatum is enriched in breast tumour tissue compared with matched healthy tissue and has been shown to promote mammary tumour growth and metastatic progression in mouse models. Current literature suggests that F. nucleatum modulates immune escape and inflammation within the tissue microenvironment, two well-defined hallmarks of cancer. Furthermore, the microbiome, and F. nucleatum specifically, has been shown to affect patient response to therapy including immune checkpoint inhibitors. These findings highlight areas of future research needed to better understand the influence of F. nucleatum in the development and treatment of breast cancer.

Type
Review
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
Copyright © The Author(s), 2023. Published by Cambridge University Press

Breast cancer

Breast cancer (BC) has exceeded lung cancer to become the most commonly diagnosed cancer worldwide, with 2.3 million cases in 2020 alone (Ref. Reference Sung1). At present, 70–80% of early-stage, non-metastatic cases are curable (Ref. Reference Harbeck2). However, secondary/metastatic BC is considered incurable with the currently available treatments. Unfortunately, in 2020 there were over 650 000 BC-related deaths worldwide, contributing to approximately 7% of cancer deaths that year (Ref. Reference Sung1). Therefore, there is an unmet clinical need to understand what causes certain cancers to resist treatment and what drives metastasis.

BC is a heterogeneous disease showing molecular and histological diversity between patients, resulting in variability in disease outcome and response to treatment. Biomarker expression has been used successfully to stratify breast tumours into molecular subgroups, guide treatment options and to develop targeted treatments such as endocrine therapies. The current molecular biomarkers with clinical significance include the oestrogen receptor (ERα), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) (Ref. Reference Harbeck2). Additionally, BCs that are ERα/PR negative and lack HER2 amplification are grouped as triple negative breast cancers (TNBCs), which lack available targeted treatment options (Ref. Reference Curigliano3), although some advances are being made in subsets of TNBC through the use of immune checkpoint inhibitors (ICIs) (Refs Reference Cortes4, Reference Emens5, Reference Schmid6, Reference Schmid7) and/or antibody-drug conjugates (Ref. Reference Bianchini8).

However, there are still limitations with current BC treatments, where patients may relapse even with subtype-specific treatment regimens. Therefore, further stratification and the identification of more effective and actionable prognostic and predictive biomarkers are required to improve patient management.

This review aims to examine the known molecular consequences of the species of bacteria Fusobacterium nucleatum (F. nucleatum) within the tumour microenvironment (TME), potentially identifying actionable pathways modulated by the bacterium that may have relevance in the BC setting.

The microbiome and cancer

The human body is host to a large population of microbes, estimated at 10–100 trillion cells (Ref. Reference Turnbaugh9), the majority of which exist within the gastrointestinal (GI) tract. Due to the development of next-generation sequencing techniques, organs which were previously believed to be sterile have been revealed to host microbial populations (Ref. Reference Nejman10). Furthermore, the human microbiome is shaped via co-evolution with the host, resulting in large compositional variations between age, sex, diet and geographical location. Therefore, the microbiome may contribute to the diversity observed in disease outcomes and treatment response between patients.

The imbalance in the relationship between the host and the microbiota (dysbiosis) is characterised by a reduction in the diversity of microbes present, and a shift towards a population in which pathogenic bacteria dominate. With the microbiome recently included as a hallmark of cancer (Ref. Reference Hanahan11) growing evidence suggests that both cancer-protective and tumour-promoting species exist, and can influence susceptibility, development, therapeutic response and metastasis (Ref. Reference Helmink12) of certain cancers. Therefore, particular members of the microbiome could be, and have already been, identified as biomarkers with clinical importance, including the human papilloma virus (HPV), hepatitis B and C and the bacterium Helicobacter pylori (Ref. Reference Cullin13).

However, more microbial species have been identified in recent years within tumour tissue as a result of the development of high-depth next-generation sequencing of bacterial 16S ribosomal RNA and more complete databases of sequenced organisms (Refs Reference Cullin13, Reference Wood and Salzberg14, Reference Gevers15, Reference Petersen16, Reference Wooley and Ye17, Reference Goodman and Gardner18). Critically, these approaches have been expanded to also characterise low-biomass intra-tumoural microbiomes, including introducing stringent pipelines which account for background noise and contamination (Ref. Reference Nejman10), and mining shotgun sequencing data generated on tumour tissue biopsies (Ref. Reference Poore19).

A number of these newly detected intra-tumoural microbes have been shown to modulate or contribute to cancer (Ref. Reference Sepich-Poore20). Conversely, some species have been exploited for cancer treatments such as probiotic treatments given alongside conventional therapy regimes or bacteria-assisted tumour-targeting therapies (Refs Reference Sedighi21, Reference Flores Bueso, Lehouritis and Tangney22).

Importantly, in a study by Nejman et al. (Ref. Reference Nejman10) which characterised the link between the microbiome and different types of solid tumours using next-generation sequencing, breast tumours were shown to have a rich and more diverse microbiome compared to the other tumour types tested, including melanoma and lung, but not including the GI tract. Furthermore, they noted variation within the dominant bacterial taxa between the ERα+, PR+ and HER2+ subtypes of BC (Ref. Reference Hanahan11). Other studies have confirmed that there is an altered microbiome in breast tumours compared with healthy tissue (Refs Reference Hieken23, Reference Esposito24, Reference Klann25, Reference Meng26, Reference Smith27, Reference Tzeng28, Reference Urbaniak29, Reference Urbaniak30), the findings of which have been reviewed previously (Refs Reference Parida and Sharma31, Reference O'Connor32). The potential to utilise the bacterial signature of breast biopsy tissue to infer malignancy status has also recently been reported (Ref. Reference Hogan33).

Breast cancer-associated bacteria have been found predominantly to reside intracellularly, both within breast tumour epithelial cells and immune cells (Refs Reference Nejman10, Reference Fu34). However, the microbiome of distant organs such as those of the GI tract can also affect carcinogenesis and progression of BC by influencing factors such as diet, obesity, levels of free circulating oestrogens and immune modulation (Refs Reference Helmink12, Reference Bodai and Nakata35, Reference Fernandez36). Moreover, the microbiome of both distant organs and the site of the tumour has been linked to local and systemic impacts on cancer chemotherapy efficacy and toxicity (Refs Reference Helmink12, Reference Bawaneh37). Studies have also shown that modulating the gut microbiome before and during chemotherapy treatment could improve efficacy and reduce the incidence of adverse events (Refs Reference Aarnoutse38, Reference Chen39), and more specifically, the gut microbiome was used as a predictive biomarker for doxorubicin responsiveness in a 4T1 murine TNBC model (Ref. Reference Bawaneh37).

Furthermore, some bacterial species have been shown to alter the TME, which is important in tumour formation, progression, metastasis and drug resistance (Refs Reference Coussens and Werb40, Reference Whiteside41). Bacterial colonisation of the tumour has been shown to activate the intertwined processes of tumour-promoting inflammation and evasion of tumour destruction by the immune system (Fig. 1) (Refs Reference Hanahan11, Reference Ismail, Hampton and Keenan42). Investigations into how the intra-tumoral bacteria may influence the breast TME are only beginning. However, remodelling of the TME in BC by bacteria has already been shown using the 4T1 syngeneic model inoculated with Escherichia coli K-12, where increased type IV collagen deposition, increased matrix metalloproteinase 9 (MMP9) expression and altered distribution of tumour-associated macrophages were observed (Ref. Reference Esposito24). Additionally, intraductal injection of mouse teats with Bacteroides fragilis resulted in increased local inflammation, tissue fibrosis and higher T-cell infiltration than in control mice (Ref. Reference Parida43).

Figure 1. The microbiome is a key regulator of the tumour microenvironment (TME). Secreted factors and ‘immunomodulatory’ factors produced by bacteria can activate damage sensors on immune cells, for example, outer membrane vesicles which contain proinflammatory molecules such as lipopolysaccharide (LPS) on Gram-negative bacteria which stimulates Toll-like receptor (TLR)-4 signalling in immune cells. This activation results in the expression of a range of chemokines and cytokines, which further influence the recruitment and behaviour of immune cells within the TME and can lead to a state of chronic inflammation. Cells present in the TME can also produce growth factors and serine proteases which induce tumour progression. Furthermore, bacteria secrete metabolites such as short chain fatty acids (SCFAs) which can interact with the TME to reshape it, and/or cause genomic instability within the cells. LPS, lipopolysaccharide; SCFA, short-chain fatty acid; ROS, reactive oxygen species; TLR, Toll-like receptor; NLR, Nod-like receptor. Figure created with BioRender.

Fusobacterium nucleatum: an overview

F. nucleatum is a Gram-negative, anaerobic, adhesive bacterium and is commonly found within the oral mucosa where it aids in biofilm formation, supporting a normal oral microenvironment (Ref. Reference Lamont, Koo and Hajishengallis44). However, F. nucleatum has also been associated with adverse pregnancy outcomes (Refs Reference Vander Haar45, Reference Parhi46), appendicitis (Ref. Reference Swidsinski47) and importantly, many tumour types (Refs Reference Nejman10, Reference Castellarin48, Reference Kostic49). For example, F. nucleatum has been reported to be a potential biomarker for populations of colorectal cancer (CRC) (Refs Reference Flanagan50, Reference Guo51, Reference Chen52, Reference Zhang53).

Studies have shown that F. nucleatum presence in tumour tissue is associated with poor overall survival (OS) in oesophageal squamous cell carcinomas (ESCC), early-stage HPV-negative tongue cancer (Ref. Reference Desai54), as well as increased metastasis in CRC patients (Refs Reference Chen52, Reference Mima55, Reference Yamamura56, Reference Kunzmann57, Reference Galeano Nino58). However, in oral squamous cell carcinoma (OSCC), F. nucleatum presence is associated with a lower recurrence rate, reduced metastases and longer OS (Ref. Reference Neuzillet59). This highlights the complexity of host–pathogen relationships, and therefore the need for individual, context-specific studies.

Methods to detect and quantify specific microbes have advanced, and the development of RNA in situ hybridisation (Refs Reference Bullman60, Reference Borgognone61, Reference Zhang62), next-generation sequencing (Refs Reference Nejman10, Reference Kostic49) and qPCR on tumour tissue (Refs Reference Castellarin48, Reference Salvucci63) has enabled detection of F. nucleatum in both high- and low-biomass tumour tissues.

F. nucleatum was identified in approximately 30% of breast tumours by Nejman et al. (Ref. Reference Nejman10), and within other BC cohorts (Refs Reference Hieken23, Reference Urbaniak29, Reference Parhi64, Reference Hoskinson65, Reference Banerjee66). Additionally, while the abundance of F. nucleatum relative to cancer cells is low, it is shown to increase in abundance in higher stage breast tumours (Ref. Reference Tzeng28). However, the clinical significance has not yet been fully elucidated for F. nucleatum in the breast. Given the findings that F. nucleatum is associated with both favourable outcomes in OSCC, and adverse outcomes in CRC and ESCC, it will be important in the future to determine the significance of F. nucleatum in the breast on survival outcomes.

Parhi et al. (Ref. Reference Parhi64) showed that F. nucleatum promoted mammary tumour growth and, critically, metastatic progression when inoculated into mice. They suggested that this effect may be mediated by suppression of T-cell infiltration into the TME and/or increased expression of MMP9 (Ref. Reference Parhi64).

The oncogenic mechanisms of F. nucleatum in cancer

An important feature of F. nucleatum is its ability to bind to a variety of host and neighbouring bacterial cells via a range of virulence factors including the Fap2 protein that binds to the sugar D-galactose-β-N-acetyl-D-galactosamine (Gal-GalNAc) (Refs Reference Sung1, Reference Harbeck2, Reference Curigliano3)(Refs Reference Parhi64, Reference Abed67) which is overexpressed in CRC and BC (Refs Reference Parhi64, Reference Abed67). Specifically, F. nucleatum binds to tumour cells, influencing downstream oncogenic and pro-metastatic signalling (Refs Reference Casasanta68, Reference Chen69, Reference Chen70, Reference Chen71, Reference Hashemi Goradel72, Reference Rubinstein73, Reference Yang74). A summary of known oncogenic F. nucleatum interactions in CRC through F. nucleatum virulence factors is summarised in Figure 2 (Refs Reference Rubinstein73, Reference Rubinstein75, Reference Xu76, Reference Lu, Yeh and Ohashi77, Reference Ellis and Kuehn78, Reference Despins79). This review expands on the influence of F. nucleatum on the TME, and how these findings may guide the research into the relationship between BC and F. nucleatum.

Figure 2. Known oncogenic pathways modulated by Fusobacterium nucleatum. F. nucleatum (shown in blue) binds to tumour cells via interaction of its Fap2 protein with D-galactose-β(1–3)-N-acetyl-D-galactosamine (Gal-GalNAc) or by FadA interacting with E-cadherin, which is enhanced by Annexin A1 (ANXA1), enabling attachment and invasion of tumour cells. F. nucleatum also secretes outer membrane vesicles (OMVs) and lipopolysaccharide (LPS) which interact with the Toll-like receptors (TLRs) to initiate downstream signalling pathways that mediate the release of inflammatory cytokines and transcription of miR-21 which is known to regulate the activity of the oncoprotein RASA1. The E-cadherin and TLR4 signalling induced by F. nucleatum binding stimulates β-catenin accumulation in the cytoplasm and its subsequent translocation to the nucleus where it upregulates transcription of oncogenes including c-MYC and Cyclin D1. Furthermore, F. nucleatum is able to aid metastasis through OMV-mediated degradation of E. cadherin, NF-κB mediated increased expression of keratin 7 (KRT7), and via induction of the inflammatory cytokines IL-8 and CXCL1. Figure created with BioRender.

Fusobacterium nucleatum and inflammation within the tumour microenvironment

Inflammation is one of the hallmarks of cancer, with up to 20% of cancers being preceded by chronic inflammation at the site (Refs Reference Grivennikov80, Reference Grivennikov, Greten and Karin81). While F. nucleatum can bind to cancer cells and activate oncogenic signalling directly, as observed in CRC, there is also evidence that F. nucleatum is able to indirectly promote tumour progression by modulating the inflammatory microenvironment.

F. nucleatum infection is closely linked to NF-κB signalling by numerous studies in multiple cell types (Refs Reference Salvucci63, Reference Rubinstein73, Reference Yang74, Reference Bui82, Reference Chen83, Reference Hung84, Reference Kostic85, Reference Nomoto86), however this link has not yet been investigated in BC. NF-κB signalling can be activated by bacteria through immune receptors including the Toll-like receptors (TLRs) to upregulate many chemokines and cytokines (described in further detail below). For example, TLR2 and TLR4 are implicated in F. nucleatum-stimulated macrophage cytokine production (Ref. Reference Park87). Constitutive activation of NF-κB signalling has been linked to inflammation and cancer (Ref. Reference Taniguchi and Karin88) via regulation of genes involved in cell proliferation, differentiation and innate and adaptive immune responses (Ref. Reference Liu89).

A number of studies have identified an inflammatory signature associated with F. nucleatum presence within CRC (Refs Reference Abed67, Reference Despins79, Reference Kostic85, Reference Proenca90). Specifically, F. nucleatum presence within human colonic tumours has been associated with the upregulation of the pro-inflammatory cytokines IL-6, IL-8 and IL-1β, among others (Refs Reference Despins79, Reference Kostic85, Reference Proenca90). It is possible that with further investigation into the breast TME, comparisons could be made between the effect of F. nucleatum in these two cancers.

In BC, upregulation of serum IL-6 levels is associated with poor prognosis (Refs Reference Shibayama91, Reference Dethlefsen, Hojfeldt and Hojman92), where hormone-sensitive tumour cells have a greater response to IL-6 (Ref. Reference Fontanini93). IL-6 has been linked to epithelial-mesenchymal transition (EMT) in BC and enhances mesenchymal stem cell recruitment in the breast TME (Refs Reference Korkaya94, Reference Madden, Szpunar and Brown95). Therefore, it is interesting that IL-6 secretion is induced by F. nucleatum infection in B lymphocytes (Ref. Reference Toussi, Liu and Massari96) and macrophages (Ref. Reference Chen83). Similarly, in CRC, Wang et al. noted that F. nucleatum infected CRC cells displayed an EMT cancer stem cell-like behaviour as a result of IL-6/STAT3 signalling (Ref. Reference Wang97).

Additionally, multiple studies have identified upregulated IL-8 as a result of F. nucleatum infection in CRC cells (Refs Reference Casasanta68, Reference Despins79, Reference Kostic85, Reference Toussi, Liu and Massari96, Reference Tang98). IL-8 in BC is associated with positive lymph node status and higher-stage tumours (Refs Reference Kozlowski99, Reference Ma100).

In colonic cells, F. nucleatum-secreted outer membrane vesicles, and the FomA porin that is present on them, induced IL-8 expression in a TLR2- and TLR4-dependent manner (Refs Reference Toussi, Liu and Massari96, Reference Engevik101), as a result of NF-κB signalling (Ref. Reference Martin-Gallausiaux102). TLRs recognise microbial products, such as lipopolysaccharide from Gram-negative bacteria like F. nucleatum and stimulate secretion of inflammatory mediators and/or activate immune cells. Extracellular vesicles were further found to induce IL-8 secretion in colonic epithelial cells in a TLR4-dependent mechanism (Ref. Reference Engevik101), again involving NF-κB signalling. F. nucleatum induces IL-8 expression through pathways involving increased reactive oxygen species (Ref. Reference Kang103), β-catenin signalling (Refs Reference Rubinstein73, Reference Rubinstein75) and invasion via its FadA adhesin (Ref. Reference Abed67), as depicted in Figure 3.

Figure 3. Known pathways induced by F. nucleatum binding that result in increased interleukin-8 (IL-8) secretion. (a) F. nucleatum infection in Caco-2 colorectal cancer cells impaired autophagic flux, which enhanced the production of TNF-α, IL-1β and IL-8 via the increase in reactive oxygen species (ROS). (b) F. nucleatum binding via its FadA adhesin to the sugar D-galactose-β(1–3)-N-acetyl-D-galactosamine (Gal-GalNAc) on colorectal cancer cells enables invasion, which further stimulates the release of IL-8 and CXCL1. (c) Outer membrane vesicles and the porin FomA secreted by F. nucleatum stimulate Toll-like receptors (TLRs) 2 and 4 on colonic epithelial cells, inducing NF-κB signalling that results in increased IL-8 secretion. (d) F. nucleatum's FadA adhesin binds to E-cadherin, activating β-catenin signalling in CRC cells, resulting in increased expression of pro-inflammatory cytokines, including IL-8. Figure created with BioRender.

Fusobacterium nucleatum and the tumour immune microenvironment

The studies highlighted in Table 1 provide abundant evidence that F. nucleatum is capable of altering the composition and actions of the immune cell population of the TME. It is possible that F. nucleatum promotes an immunosuppressive TME, enabling tumour cell escape from immune surveillance. While research into how the presence of F. nucleatum alters the immune response to other cancers is more advanced, little is known at this time with respect to the impact of F. nucleatum on the TME in BC. Given the importance of the immune response to BC and its impact on survival, drug efficacy and metastatic potential (Ref. Reference Badr, Berditchevski and Shaaban104), the presence of F. nucleatum and its known ability to alter the tumour immune microenvironment is an important area of future research.

Table 1. The effect of F. nucleatum on immune cells from different studies

AI-2; autoinducer-2, BC; breast cancer, CbpF; chlorine-binding protein; CCL20, chemokine (C-C motif) ligand 20; CD, cluster of differentiation; CEACAM1, CEA cell adhesion molecule 1; c-MYC, cellular-MYC; CRC, colorectal cancer; DNA, deoxyribonucleic acid; ESCC, oesophageal squamous cell carcinoma; FFAR2, free fatty acid receptor 2; IL-1β, interleukin 1β; IL-6, interleukin-6; KIR2DL1, killer cell immunoglobulin-like receptor 2DL1; NF-κB, nuclear factor kappa B; NK, natural killer cell; OSCC, oral squamous cell carcinoma; p-STAT3, phospho-signal transducer and activator of transcription 3; RNA, ribonucleic acid; SCFA, short-chain fatty acid; S100A9, S100 calcium-binding protein A9; TIGIT, T-cell immunoreceptor with Ig and ITIM domains; TLR4, Toll-like receptor 4; TNFSF9, tumour necrosis factor ligand superfamily member 9; TOX, thymocyte selection-associated high mobility group box protein.

Fusobacterium nucleatum and tumour response to treatment

Treatment of BC is multi-faceted, using a combination of surgery, radiotherapy and/or systemic therapy guided by the cancer molecular subtype (Ref. Reference Harbeck2). However, drug resistance (intrinsic and acquired) often develops. F. nucleatum may influence treatment response in CRC, ESCC, OSCC and rectal adenocarcinoma. Given the presence of F. nucleatum in approximately 20% of BCs (Ref. Reference Nejman10), the importance of F. nucleatum as a biomarker which may aid in predicting response of BC subtypes to their treatments warrants further investigation. Additionally, F. nucleatum itself presents a potential therapeutic target, with antibiotic treatment successfully restricting growth and metastasis of mammary tumours in a mouse model, where the mice were inoculated with F. nucleatum (Ref. Reference Parhi64).

Fusobacterium nucleatum and chemotherapy resistance

As chemoresistance in BC is not yet fully understood, understanding mechanisms underlying drug resistance is vital to improve therapeutic approaches and clinical outcomes. Importantly, F. nucleatum has been reported to contribute to chemoresistance within CRC, ESCC and OSCC (Refs Reference Liu122, Reference Rui123, Reference Yu124, Reference Zhang125).

In CRC cell lines, F. nucleatum was shown to promote chemoresistance to oxaliplatin and 5-fluorouracil (5-FU) by upregulating autophagy (Ref. Reference Yu124) in a TLR4- and MYD88-dependent signalling pathway, and by preventing apoptosis via upregulation of ANO1 (Ref. Reference Lu126) or BIRC3 (Ref. Reference Zhang125). Additionally, F. nucleatum promotes chemoresistance to 5-FU as well as cisplatin and docetaxel in ESCC (Refs Reference Wang116, Reference Liu122, Reference Liang127) via upregulation of autophagy and preventing apoptosis. It is important to note that 5-FU is often used in BC treatment as a part of the FEC regime (5-FU, epirubicin and cyclophosphamide), in combination with docetaxel. Additionally, cisplatin is used in the neo-adjuvant setting for TNBC treatment (Ref. Reference Silver128). Furthermore, F. nucleatum induced autophagy is linked to CRC metastasis (Ref. Reference Chen70). These studies correlate with the observed poor patient response to neoadjuvant chemotherapy in ESCC tumours with high abundance of F. nucleatum (Refs Reference Yamamura129, Reference Wang130). Similarly, F. nucleatum was also shown to be enriched in OSCCs which were unresponsive to chemotherapy (Ref. Reference Rui123).

Fusobacterium nucleatum and radiotherapy resistance

Serna et al. (Ref. Reference Serna131) showed that chemotherapy and radiotherapy treatment was able to shift rectal adenocarcinoma tumours from F. nucleatum-positive to F. nucleatum-negative, which then showed improved relapse-free survival. However, any persistent F. nucleatum positivity correlated with a higher risk of relapse development.

Additionally, Dong et al. (Ref. Reference Dong132) demonstrated that oral administration of F. nucleatum in CRC mice impaired the efficiency of radiotherapy, promoted colonic inflammation, increased the volume and number of tumours present and further increased metastases.

With radiotherapy being a major adjuvant therapy for eradication of BCs, F. nucleatum within the tumour tissue may be an important biomarker that predicts treatment response to radiotherapy.

Fusobacterium nucleatum and immunotherapy

Immune checkpoint therapy inhibits the interaction between a T-cell inhibitory receptor and its canonical ligand(s), allowing T lymphocytes to elicit antitumour responses (Ref. Reference Topalian, Drake and Pardoll133). For example, programmed cell death protein 1 (PD-1) when bound to its ligand PD-L1 inhibits T-cell activation (Ref. Reference Ahmadzadeh134). While BC is considered to be less sensitive to immunotherapy than other cancers (Refs Reference Cardoso135, Reference Solinas136, Reference Parkes137), PD-L1 is still expressed on a small subset of BC tumour cells (Refs Reference Polonia138, Reference Humphries139), and is associated with TNBC and HER2 overexpressing BCs (Refs Reference Humphries139, Reference Bertucci and Goncalves140). Furthermore, treatment with ICIs such as atezolizumab has been approved for metastatic TNBC, and pembrolizumab improved clinical outcome for metastatic TNBC and high-risk early-stage TNBC (Refs Reference Heimes and Schmidt141, Reference Adams142, Reference Kwapisz143, Reference Schmid144, Reference Zacharakis145). Recently, the FDA has granted accelerated approval to pembrolizumab in combination with chemotherapy for high-risk early-stage TNBC and for metastatic TNBC whose tumours express PD-L1. Therefore, the impact that F. nucleatum has on altering response to immunotherapy across BC subgroups should be further investigated, as well as its potential as a biomarker able to identify patients which will benefit from it.

In both patients and mice with CRC, Gao et al. found that F. nucleatum presence was correlated with improved response to PD-1/PD-L1 blockade treatment (Ref. Reference Gao146). In the murine model of CRC, treatment with F. nucleatum enhanced anti-PD-L1 treatment response, and further improved survival (Ref. Reference Gao146). Moreover, when F. nucleatum treatment was combined with anti-PD-L1 treatment, there was a significant increase in the amount of CD8+ T lymphocytes in the TME. Cancers with higher populations of CD8+ T lymphocytes are expected to have the greatest response to immunotherapy (Ref. Reference Trujillo147). Therefore, it is possible to hypothesise that the alterations induced by F. nucleatum in CRC may result in a TME which responds more effectively to immunotherapy. However, a higher abundance of F. nucleatum in the patient's airways has been associated with a worse response of lung cancer to PD-1 blockade treatment (Ref. Reference Chu148).

Conclusions and future directions

F. nucleatum has been identified as a bacterial species which colonises the breast and recent findings indicate that it may contribute to BC progression and metastatic development (Ref. Reference Parhi64). However, the underlying pathogenic mechanisms are poorly understood, with few studies investigating the potential role of F. nucleatum in BC patient cohorts. Typically, F. nucleatum has been identified in approximately 20–30% of BC tumours (Refs Reference Nejman10, Reference Urbaniak29, Reference Parhi64), but correlation with clinical characteristics such as tumour stage or BC subgroup requires further investigation.

The literature from research into other cancer types, including CRC, indicates that F. nucleatum is able to modulate the local TME, promoting an inflammatory state and further interacting with and influencing infiltrating immune cells. The question of whether the presence of F. nucleatum in the TME of breast carcinomas will show the same trends in inflammation and immunomodulation requires further investigation. In particular, advanced in vitro models such as organoids could be beneficial to recapitulate how the hypoxic environment of the tumour influences the survival and growth of the anaerobic F. nucleatum. Additionally, in vivo models should be considered for further investigating the relationship between F. nucleatum in breast tumours with the tumour immune microenvironment (Ref. Reference Parhi64).

Multiple protocols have been suggested in order to quantify the presence of F. nucleatum in cancer patients, for example, a faecal F. nucleatum-based assay for CRC (Ref. Reference Huang, Peng and Xie149), and qPCR of F. nucleatum DNA in tumour tissue (Refs Reference Flanagan50, Reference Datorre150, Reference de Carvalho151, Reference Tunsjo152, Reference Yamamura153). However, current literature highlights the difficulties in detecting microbial DNA from human host tissues, which is exacerbated in low microbial biomass tumour tissues such as is seen in the breast (Refs Reference Bodai and Nakata35, Reference de Goffau154, Reference Walker155, Reference Walker, Tangney and Claesson156). Before F. nucleatum can be used as a biomarker for any cancer type, a sensitive, yet cost-effective assay must be developed to detect and quantify F. nucleatum in patients. Salivary F. nucleatum DNA has been identified as a non-invasive biomarker for CRC and gastric cancer diagnosis (Refs Reference Zhang53, Reference Chen157). Further research is required to determine if these findings could also apply to other F. nucleatum-linked cancers, including breast.

Targeting F. nucleatum in the tumour could potentially introduce an exciting novel treatment option. Parhi et al. (Ref. Reference Parhi64) showed that antibiotic treatment of a BC mouse model inoculated with F. nucleatum eliminated F. nucleatum from the tumour and further suppressed F. nucleatum-induced tumour growth. It is therefore tempting to consider antibiotics adjunct to current BC treatments to target tumour-promoting bacteria. However, given the role of the patient's microbiome in influencing drug efficacy (Refs Reference Helmink12, Reference Bodai and Nakata35, Reference Bawaneh37, Reference Aarnoutse38, Reference Gopalakrishnan158, Reference Routy159, Reference Lehouritis160), broad microbe-targeting treatments may not be beneficial. Interestingly, a F. nucleatum-specific bacteriophage, FNU1, has been recently suggested as a means to eradicate the oncobacterium from the tumour (Ref. Reference Kabwe161). Strong evidence supports the influence of the gut microbiome in response to cancer therapy, most notably ICIs (Ref. Reference Li162). Given the increasing use of ICIs in BC, especially for TNBC (Refs Reference Heimes and Schmidt141, Reference Adams142, Reference Kwapisz143, Reference Tarantino163), the potential interaction between F. nucleatum within the breast and ICI therapy (Ref. Reference Gao146) is an especially interesting area of future research.

In conclusion, by better understanding the consequences of the presence of this bacterium, it will provide valuable insights into the role of the microbiota in BC progression and how it influences treatment efficacy in patients.

References

Sung, H et al. (2021) Global cancer statistics 2020: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA: A Cancer Journal for Clinicians 71, 209249.Google ScholarPubMed
Harbeck, N et al. (2019) Breast cancer. Nature Reviews Disease Primers 5, 66.Google ScholarPubMed
Curigliano, G et al. (2017) De-escalating and escalating treatments for early-stage breast cancer: the St. Gallen international expert consensus conference on the primary therapy of early breast cancer 2017. Annals of Oncology 28, 17001712.CrossRefGoogle ScholarPubMed
Cortes, J et al. (2020) Pembrolizumab plus chemotherapy versus placebo plus chemotherapy for previously untreated locally recurrent inoperable or metastatic triple-negative breast cancer (KEYNOTE-355): a randomised, placebo-controlled, double-blind, phase 3 clinical trial. Lancet 396, 18171828.CrossRefGoogle ScholarPubMed
Emens, LA et al. (2020) Trastuzumab emtansine plus atezolizumab versus trastuzumab emtansine plus placebo in previously treated, HER2-positive advanced breast cancer (KATE2): a phase 2, multicentre, randomised, double-blind trial. The Lancet. Oncology 21, 12831295.CrossRefGoogle ScholarPubMed
Schmid, P et al. (2018) Atezolizumab and nab-paclitaxel in advanced triple-negative breast cancer. New England Journal of Medicine 379, 21082121.CrossRefGoogle ScholarPubMed
Schmid, P et al. (2020) Pembrolizumab plus chemotherapy as neoadjuvant treatment of high-risk, early-stage triple-negative breast cancer: results from the phase 1b open-label, multicohort KEYNOTE-173 study. Annals of Oncology 31, 569581.CrossRefGoogle ScholarPubMed
Bianchini, G et al. (2022) Treatment landscape of triple-negative breast cancer – expanded options, evolving needs. Nature Reviews. Clinical Oncology 19, 91113.CrossRefGoogle ScholarPubMed
Turnbaugh, PJ et al. (2007) The human microbiome project. Nature 449, 804810.CrossRefGoogle ScholarPubMed
Nejman, D et al. (2020) The human tumor microbiome is composed of tumor type-specific intracellular bacteria. Science 368, 973980.CrossRefGoogle ScholarPubMed
Hanahan, D (2022) Hallmarks of cancer: new dimensions. Cancer Discovery 12, 3146.CrossRefGoogle ScholarPubMed
Helmink, BA et al. (2019) The microbiome, cancer, and cancer therapy. Nature Medicine 25, 377388.CrossRefGoogle ScholarPubMed
Cullin, N et al. (2021) Microbiome and cancer. Cancer Cell 39, 13171341.CrossRefGoogle ScholarPubMed
Wood, DE and Salzberg, SL (2014) Kraken: ultrafast metagenomic sequence classification using exact alignments. Genome Biology 15, R46.CrossRefGoogle ScholarPubMed
Gevers, D et al. (2012) Bioinformatics for the human microbiome project. PLoS Computational Biology 8, e1002779.CrossRefGoogle ScholarPubMed
Petersen, TN et al. (2017) MGmapper: reference based mapping and taxonomy annotation of metagenomics sequence reads. PLoS ONE 12, e0176469.CrossRefGoogle ScholarPubMed
Wooley, JC and Ye, Y (2009) Metagenomics: facts and artifacts, and computational challenges*. Journal of Computer Science and Technology 25, 7181.CrossRefGoogle ScholarPubMed
Goodman, B and Gardner, H (2018) The microbiome and cancer. The Journal of Pathology 244, 667676.CrossRefGoogle ScholarPubMed
Poore, GD et al. (2020) Microbiome analyses of blood and tissues suggest cancer diagnostic approach. Nature 579, 567574.CrossRefGoogle ScholarPubMed
Sepich-Poore, GD et al. (2021) The microbiome and human cancer. Science 371, 6536.CrossRefGoogle ScholarPubMed
Sedighi, M et al. (2019) Therapeutic bacteria to combat cancer; current advances, challenges, and opportunities. Cancer Medicine 8, 31673181.Google ScholarPubMed
Flores Bueso, Y, Lehouritis, P and Tangney, M (2018) In situ biomolecule production by bacteria; a synthetic biology approach to medicine. Journal of Controlled Release 275, 217228.CrossRefGoogle ScholarPubMed
Hieken, TJ et al. (2016) The microbiome of aseptically collected human breast tissue in benign and malignant disease. Scientific Reports 6, 30751.CrossRefGoogle ScholarPubMed
Esposito, MV et al. (2022) Microbiome composition indicate dysbiosis and lower richness in tumor breast tissues compared to healthy adjacent paired tissue, within the same women. BMC Cancer 22, 30.CrossRefGoogle ScholarPubMed
Klann, E et al. (2020) Microbiota composition in bilateral healthy breast tissue and breast tumors. Cancer Causes & Control 31, 10271038.CrossRefGoogle ScholarPubMed
Meng, S et al. (2018) Study of microbiomes in aseptically collected samples of human breast tissue using needle biopsy and the potential role of in situ tissue microbiomes for promoting malignancy. Frontiers in Oncology 8, 318.CrossRefGoogle ScholarPubMed
Smith, A et al. (2019) Distinct microbial communities that differ by race, stage, or breast-tumor subtype in breast tissues of non-Hispanic Black and non-Hispanic White women. Scientific Reports 9, 11940.CrossRefGoogle ScholarPubMed
Tzeng, A et al. (2021) Human breast microbiome correlates with prognostic features and immunological signatures in breast cancer. Genome Medicine 13, 60.CrossRefGoogle ScholarPubMed
Urbaniak, C et al. (2014) Microbiota of human breast tissue. Applied and Environmental Microbiology 80, 30073014.CrossRefGoogle ScholarPubMed
Urbaniak, C et al. (2016) The microbiota of breast tissue and its association with breast cancer. Applied and Environmental Microbiology 82, 50395048.CrossRefGoogle ScholarPubMed
Parida, S and Sharma, D (2019) The power of small changes: comprehensive analyses of microbial dysbiosis in breast cancer. Biochimica et Biophysica Acta, Reviews on Cancer 1871, 392405.CrossRefGoogle ScholarPubMed
O'Connor, H et al. (2018) Resident bacteria in breast cancer tissue: pathogenic agents or harmless commensals? Discovery Medicine 26, 93102.Google ScholarPubMed
Hogan, G et al. (2021) Biopsy bacterial signature can predict patient tissue malignancy. Scientific Reports 11, 18535.CrossRefGoogle ScholarPubMed
Fu, A et al. (2022) Tumor-resident intracellular microbiota promotes metastatic colonization in breast cancer. Cell 185, 13561372, e26.CrossRefGoogle ScholarPubMed
Bodai, BI and Nakata, TE (2020) Breast cancer: lifestyle, the human gut microbiota/microbiome, and survivorship. The Permanente Journal 24, 19.129.CrossRefGoogle ScholarPubMed
Fernandez, L et al. (2020) The microbiota of the human mammary ecosystem. Frontiers in cellular and infection microbiology 10, 586667.CrossRefGoogle ScholarPubMed
Bawaneh, A et al. (2022) Intestinal microbiota influence doxorubicin responsiveness in triple-negative breast cancer. Cancers 14, 4849.CrossRefGoogle ScholarPubMed
Aarnoutse, R et al. (2019) The clinical link between human intestinal microbiota and systemic cancer therapy. International journal of molecular sciences 20, 4145.CrossRefGoogle ScholarPubMed
Chen, J et al. (2019) The microbiome and breast cancer: a review. Breast Cancer Research and Treatment 178, 493496.CrossRefGoogle ScholarPubMed
Coussens, LM and Werb, Z (2002) Inflammation and cancer. Nature 420, 860867.CrossRefGoogle ScholarPubMed
Whiteside, TL (2008) The tumor microenvironment and its role in promoting tumor growth. Oncogene 27, 59045912.CrossRefGoogle ScholarPubMed
Ismail, S, Hampton, MB and Keenan, JI (2003) Helicobacter pylori outer membrane vesicles modulate proliferation and interleukin-8 production by gastric epithelial cells. Infection and Immunity 71, 56705675.CrossRefGoogle ScholarPubMed
Parida, S et al. (2021) A procarcinogenic colon microbe promotes breast tumorigenesis and metastatic progression and concomitantly activates notch and beta-catenin axes. Cancer Discovery 11, 11381157.CrossRefGoogle ScholarPubMed
Lamont, RJ, Koo, H and Hajishengallis, G (2018) The oral microbiota: dynamic communities and host interactions. Nature Reviews Microbiology 16, 745759.CrossRefGoogle ScholarPubMed
Vander Haar, EL et al. (2018) Fusobacterium nucleatum and adverse pregnancy outcomes: epidemiological and mechanistic evidence. Anaerobe 50, 5559.CrossRefGoogle ScholarPubMed
Parhi, L et al. (2022) Placental colonization by Fusobacterium nucleatum is mediated by binding of the Fap2 lectin to placentally displayed Gal-GalNAc. Cell Reports 38, 110537.CrossRefGoogle ScholarPubMed
Swidsinski, A et al. (2011) Acute appendicitis is characterised by local invasion with Fusobacterium nucleatum/necrophorum. Gut 60, 3440.CrossRefGoogle ScholarPubMed
Castellarin, M et al. (2012) Fusobacterium nucleatum infection is prevalent in human colorectal carcinoma. Genome Research 22, 299306.CrossRefGoogle ScholarPubMed
Kostic, AD et al. (2012) Genomic analysis identifies association of Fusobacterium with colorectal carcinoma. Genome Research 22, 292298.CrossRefGoogle ScholarPubMed
Flanagan, L et al. (2014) Fusobacterium nucleatum associates with stages of colorectal neoplasia development, colorectal cancer and disease outcome. European Journal of Clinical Microbiology & Infectious Diseases 33, 13811390.CrossRefGoogle ScholarPubMed
Guo, S et al. (2018) A simple and novel fecal biomarker for colorectal cancer: ratio of Fusobacterium nucleatum to probiotics populations, based on their antagonistic effect. Clinical Chemistry 64, 13271337.CrossRefGoogle ScholarPubMed
Chen, WD et al. (2022) Fusobacterium nucleatum is a risk factor for metastatic colorectal cancer. Current Medical Science 42, 538547.CrossRefGoogle ScholarPubMed
Zhang, X et al. (2022) Salivary Fusobacterium nucleatum serves as a potential biomarker for colorectal cancer. iScience 25, 104203.CrossRefGoogle ScholarPubMed
Desai, S et al. (2022) Fusobacterium nucleatum is associated with inflammation and poor survival in early-stage HPV-negative tongue cancer. NAR Cancer 4, zcac006.CrossRefGoogle ScholarPubMed
Mima, K et al. (2016) Fusobacterium nucleatum in colorectal carcinoma tissue and patient prognosis. Gut 65, 19731980.CrossRefGoogle ScholarPubMed
Yamamura, K et al. (2016) Human microbiome Fusobacterium nucleatum in esophageal cancer tissue is associated with prognosis. Clinical Cancer Research 22, 55745581.CrossRefGoogle ScholarPubMed
Kunzmann, AT et al. (2019) Fusobacterium nucleatum tumor DNA levels are associated with survival in colorectal cancer patients. European Journal of Clinical Microbiology & Infectious Diseases 38, 18911899.CrossRefGoogle ScholarPubMed
Galeano Nino, JL et al. (2022) Effect of the intratumoral microbiota on spatial and cellular heterogeneity in cancer. Nature 611, 810817.CrossRefGoogle ScholarPubMed
Neuzillet, C et al. (2021) Prognostic value of intratumoral Fusobacterium nucleatum and association with immune-related gene expression in oral squamous cell carcinoma patients. Scientific Reports 11, 7870.CrossRefGoogle ScholarPubMed
Bullman, S et al. (2017) Analysis of Fusobacterium persistence and antibiotic response in colorectal cancer. Science 358, 14431448.CrossRefGoogle ScholarPubMed
Borgognone, A et al. (2021) Performance of 16S metagenomic profiling in formalin-fixed paraffin-embedded versus fresh-frozen colorectal cancer tissues. Cancers 13, 5421.CrossRefGoogle ScholarPubMed
Zhang, N et al. (2021) Clinical significance of Fusobacterium nucleatum infection and regulatory T cell enrichment in esophageal squamous cell carcinoma. Pathology & Oncology Research 27, 1609846.CrossRefGoogle ScholarPubMed
Salvucci, M et al. (2021) Patients with mesenchymal tumours and high Fusobacteriales prevalence have worse prognosis in colorectal cancer (CRC). Gut 71, 16001612.Google ScholarPubMed
Parhi, L et al. (2020) Breast cancer colonization by Fusobacterium nucleatum accelerates tumor growth and metastatic progression. Nature Communications 11, 3259.CrossRefGoogle ScholarPubMed
Hoskinson, C et al. (2022) Composition and functional potential of the human mammary microbiota prior to and following breast tumor diagnosis. mSystems 7, e0148921.CrossRefGoogle ScholarPubMed
Banerjee, S et al. (2021) Prognostic correlations with the microbiome of breast cancer subtypes. Cell Death & Disease 12, 831.CrossRefGoogle ScholarPubMed
Abed, J et al. (2016) Fap2 mediates Fusobacterium nucleatum colorectal adenocarcinoma enrichment by binding to tumor-expressed Gal-GalNAc. Cell Host & Microbe 20, 215225.CrossRefGoogle ScholarPubMed
Casasanta, MA et al. (2020) Fusobacterium nucleatum host-cell binding and invasion induces IL-8 and CXCL1 secretion that drives colorectal cancer cell migration. Science Signaling 13, eaba9157.CrossRefGoogle ScholarPubMed
Chen, S et al. (2020) Fusobacterium nucleatum promotes colorectal cancer metastasis by modulating KRT7-AS/KRT7. Gut Microbes 11, 511525.CrossRefGoogle ScholarPubMed
Chen, Y et al. (2020) Fusobacterium nucleatum promotes metastasis in colorectal cancer by activating autophagy signaling via the upregulation of CARD3 expression. Theranostics 10, 323339.CrossRefGoogle ScholarPubMed
Chen, Y et al. (2017) Invasive Fusobacterium nucleatum activates beta-catenin signaling in colorectal cancer via a TLR4/P-PAK1 cascade. Oncotarget 8, 3180231814.CrossRefGoogle Scholar
Hashemi Goradel, N et al. (2019) Fusobacterium nucleatum and colorectal cancer: a mechanistic overview. Journal of Cellular Physiology 234, 23372344.CrossRefGoogle ScholarPubMed
Rubinstein, MR et al. (2013) Fusobacterium nucleatum promotes colorectal carcinogenesis by modulating E-cadherin/beta-catenin signaling via its FadA adhesin. Cell Host & Microbe 14, 195206.CrossRefGoogle ScholarPubMed
Yang, Y et al. (2017) Fusobacterium nucleatum increases proliferation of colorectal cancer cells and tumor development in mice by activating Toll-like receptor 4 signaling to nuclear factor-kappaB, and up-regulating expression of microRNA-21. Gastroenterology 152, 851866, e24.CrossRefGoogle ScholarPubMed
Rubinstein, MR et al. (2019) Fusobacterium nucleatum promotes colorectal cancer by inducing Wnt/beta-catenin modulator Annexin A1. EMBO Reports 20, p.e47638.CrossRefGoogle ScholarPubMed
Xu, M et al. (2007) FadA from Fusobacterium nucleatum utilizes both secreted and nonsecreted forms for functional oligomerization for attachment and invasion of host cells. Journal of Biological Chemistry 282, 2500025009.CrossRefGoogle ScholarPubMed
Lu, YC, Yeh, WC and Ohashi, PS (2008) LPS/TLR4 signal transduction pathway. Cytokine 42, 145151.CrossRefGoogle ScholarPubMed
Ellis, TN and Kuehn, MJ (2010) Virulence and immunomodulatory roles of bacterial outer membrane vesicles. Microbiology and Molecular Biology Reviews 74, 8194.CrossRefGoogle ScholarPubMed
Despins, CA et al. (2021) Modulation of the host cell transcriptome and epigenome by Fusobacterium nucleatum. mBio 12, e0206221.CrossRefGoogle ScholarPubMed
Grivennikov, SI (2013) Inflammation and colorectal cancer: colitis-associated neoplasia. Seminars in Immunopathology 35, 229244.CrossRefGoogle ScholarPubMed
Grivennikov, SI, Greten, FR and Karin, M (2010) Immunity, inflammation, and cancer. Cell 140, 883899.CrossRefGoogle ScholarPubMed
Bui, FQ et al. (2016) Fusobacterium nucleatum infection of gingival epithelial cells leads to NLRP3 inflammasome-dependent secretion of IL-1beta and the danger signals ASC and HMGB1. Cellular Microbiology 18, 970981.CrossRefGoogle ScholarPubMed
Chen, T et al. (2018) Fusobacterium nucleatum promotes M2 polarization of macrophages in the microenvironment of colorectal tumours via a TLR4-dependent mechanism. Cancer Immunology Immunotherapy 67, 16351646.Google Scholar
Hung, SC et al. (2018) NLRX1 modulates differentially NLRP3 inflammasome activation and NF-kappaB signaling during Fusobacterium nucleatum infection. Microbes and Infection 20, 615625.CrossRefGoogle ScholarPubMed
Kostic, AD et al. (2013) Fusobacterium nucleatum potentiates intestinal tumorigenesis and modulates the tumor-immune microenvironment. Cell Host & Microbe 14, 207215.CrossRefGoogle ScholarPubMed
Nomoto, D et al. (2022) Fusobacterium nucleatum promotes esophageal squamous cell carcinoma progression via the NOD1/RIPK2/NF-kappaB pathway. Cancer Letters 530, 5967.CrossRefGoogle ScholarPubMed
Park, SR et al. (2014) Diverse Toll-like receptors mediate cytokine production by Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans in macrophages. Infection and Immunity 82, 19141920.CrossRefGoogle ScholarPubMed
Taniguchi, K and Karin, M (2018) NF-kappaB, inflammation, immunity and cancer: coming of age. Nature Reviews Immunology 18, 309324.CrossRefGoogle ScholarPubMed
Liu, T et al. (2017) NF-kappaB signaling in inflammation. Signal Transduction and Targeted Therapy 2, 19.CrossRefGoogle ScholarPubMed
Proenca, MA et al. (2018) Relationship between Fusobacterium nucleatum, inflammatory mediators and microRNAs in colorectal carcinogenesis. World Journal of Gastroenterology 24, 53515365.CrossRefGoogle ScholarPubMed
Shibayama, O et al. (2014) Association between adjuvant regional radiotherapy and cognitive function in breast cancer patients treated with conservation therapy. Cancer Medicine 3, 702709.CrossRefGoogle ScholarPubMed
Dethlefsen, C, Hojfeldt, G and Hojman, P (2013) The role of intratumoral and systemic IL-6 in breast cancer. Breast Cancer Research and Treatment 138, 657664.CrossRefGoogle ScholarPubMed
Fontanini, G et al. (1999) Expression of interleukin 6 (IL-6) correlates with oestrogen receptor in human breast carcinoma. British Journal of Cancer 80, 579584.CrossRefGoogle ScholarPubMed
Korkaya, H et al. (2012) Activation of an IL6 inflammatory loop mediates trastuzumab resistance in HER2+ breast cancer by expanding the cancer stem cell population. Molecular Cell 47, 570584.CrossRefGoogle ScholarPubMed
Madden, KS, Szpunar, MJ and Brown, EB (2011) beta-Adrenergic receptors (beta-AR) regulate VEGF and IL-6 production by divergent pathways in high beta-AR-expressing breast cancer cell lines. Breast Cancer Research and Treatment 130, 747758.CrossRefGoogle ScholarPubMed
Toussi, DN, Liu, X and Massari, P (2012) The FomA porin from Fusobacterium nucleatum is a Toll-like receptor 2 agonist with immune adjuvant activity. Clinical and Vaccine Immunology 19, 10931101.CrossRefGoogle ScholarPubMed
Wang, Q et al. (2020) Fusobacterium nucleatum produces cancer stem cell characteristics via EMT-resembling variations. International Journal of Clinical and Experimental Pathology 13, 18191828.Google ScholarPubMed
Tang, B et al. (2016) Fusobacterium nucleatum-induced impairment of autophagic flux enhances the expression of proinflammatory cytokines via ROS in Caco-2 cells. PLoS ONE 11, e0165701.CrossRefGoogle ScholarPubMed
Kozlowski, L et al. (2003) Concentration of interleukin-6 (IL-6), interleukin-8 (IL-8) and interleukin-10 (IL-10) in blood serum of breast cancer patients. Roczniki Akademii Medycznej W Bialymstoku (1995) 48, 8284.Google ScholarPubMed
Ma, Y et al. (2017) IL-6, IL-8 and TNF-alpha levels correlate with disease stage in breast cancer patients. Advances in Clinical and Experimental Medicine 26, 421426.CrossRefGoogle ScholarPubMed
Engevik, MA et al. (2021) Fusobacterium nucleatum secretes outer membrane vesicles and promotes intestinal inflammation. mBio 12, e02706e02720.CrossRefGoogle ScholarPubMed
Martin-Gallausiaux, C et al. (2020) Fusobacterium nucleatum extracellular vesicles modulate gut epithelial cell innate immunity via FomA and TLR2. Frontiers in Immunology 11, 583644.CrossRefGoogle ScholarPubMed
Kang, W et al. (2019) Fusobacterium nucleatum facilitates apoptosis, ROS generation, and inflammatory cytokine production by activating AKT/MAPK and NF-kappaB signaling pathways in human gingival fibroblasts. Oxidative Medicine and Cellular Longevity 2019, 1681972.CrossRefGoogle ScholarPubMed
Badr, NM, Berditchevski, F and Shaaban, AM (2020) The immune microenvironment in breast carcinoma: predictive and prognostic role in the neoadjuvant setting. Pathobiology 87, 6174.CrossRefGoogle ScholarPubMed
Shenker, BJ and DiRienzo, JM (1984) Suppression of human peripheral blood lymphocytes by Fusobacterium nucleatum. Journal of Immunology 132, 23572362.CrossRefGoogle ScholarPubMed
Jewett, A et al. (2000) Induction of apoptotic cell death in peripheral blood mononuclear and polymorphonuclear cells by an oral bacterium, Fusobacterium nucleatum. Infection and Immunity 68, 18931898.CrossRefGoogle ScholarPubMed
Shenker, BJ and Datar, S (1995) Fusobacterium nucleatum inhibits human T-cell activation by arresting cells in the mid-G1 phase of the cell cycle. Infection and Immunity 63, 48304836.CrossRefGoogle ScholarPubMed
Kaplan, CW et al. (2010) Fusobacterium nucleatum outer membrane proteins Fap2 and RadD induce cell death in human lymphocytes. Infection and Immunity 78, 47734778.CrossRefGoogle ScholarPubMed
Mima, K et al. (2015) Fusobacterium nucleatum and T cells in colorectal carcinoma. JAMA Oncology 1, 653661.CrossRefGoogle Scholar
Chen, T et al. (2018) TOX expression decreases with progression of colorectal cancers and is associated with CD4 T-cell density and Fusobacterium nucleatum infection. Human Pathology 79, 93101.CrossRefGoogle ScholarPubMed
Gur, C et al. (2015) Binding of the Fap2 protein of Fusobacterium nucleatum to human inhibitory receptor TIGIT protects tumors from immune cell attack. Immunity 42, 344355.CrossRefGoogle ScholarPubMed
Gur, C et al. (2019) Fusobacterium nucleatum supresses anti-tumor immunity by activating CEACAM1. Oncoimmunology 8, e1581531.CrossRefGoogle ScholarPubMed
Galaski, J et al. (2021) Fusobacterium nucleatum CbpF mediates inhibition of T cell function through CEACAM1 activation. Frontiers in Cellular and Infection Microbiology 11, 692544.CrossRefGoogle ScholarPubMed
Jia, YP et al. (2017) TLR2/TLR4 activation induces Tregs and suppresses intestinal inflammation caused by Fusobacterium nucleatum in vivo. PLoS ONE 12, e0186179.CrossRefGoogle ScholarPubMed
Brennan, CA et al. (2021) Fusobacterium nucleatum drives a pro-inflammatory intestinal microenvironment through metabolite receptor-dependent modulation of IL-17 expression. Gut Microbes 13, 1987780.CrossRefGoogle ScholarPubMed
Wang, X et al. (2022) Clinical impact of Fn-induced high expression of KIR2DL1 in CD8 T lymphocytes in oesophageal squamous cell carcinoma. Annals of Medicine 54, 5162.CrossRefGoogle ScholarPubMed
Kim, YJ et al. (2021) Impact of Fusobacterium nucleatum in the gastrointestinal tract on natural killer cells. World Journal of Gastroenterology 27, 48794889.CrossRefGoogle ScholarPubMed
Park, HE et al. (2017) Intratumoral Fusobacterium nucleatum abundance correlates with macrophage infiltration and CDKN2A methylation in microsatellite-unstable colorectal carcinoma. Virchows Archiv 471, 329336.CrossRefGoogle ScholarPubMed
Xu, C et al. (2021) Fusobacterium nucleatum promotes colorectal cancer metastasis through miR-1322/CCL20 axis and M2 polarization. Gut Microbes 13, 1980347.CrossRefGoogle ScholarPubMed
Hu, L et al. (2021) Fusobacterium nucleatum facilitates M2 macrophage polarization and colorectal carcinoma progression by activating TLR4/NF-kappaB/S100A9 cascade. Frontiers in Immunology 12, 658681.CrossRefGoogle ScholarPubMed
Wu, J et al. (2019) Autoinducer-2 of Fusobacterium nucleatum promotes macrophage M1 polarization via TNFSF9/IL-1beta signaling. International Immunopharmacology 74, 105724.CrossRefGoogle ScholarPubMed
Liu, Y et al. (2021) Fusobacterium nucleatum confers chemoresistance by modulating autophagy in oesophageal squamous cell carcinoma. British Journal of Cancer 124, 963974.CrossRefGoogle ScholarPubMed
Rui, M et al. (2021) The baseline oral microbiota predicts the response of locally advanced oral squamous cell carcinoma patients to induction chemotherapy: a prospective longitudinal study. Radiotherapy & Oncology 164, 8391.CrossRefGoogle ScholarPubMed
Yu, T et al. (2017) Fusobacterium nucleatum promotes chemoresistance to colorectal cancer by modulating autophagy. Cell 170, 548563. e16.CrossRefGoogle ScholarPubMed
Zhang, S et al. (2019) Fusobacterium nucleatum promotes chemoresistance to 5-fluorouracil by upregulation of BIRC3 expression in colorectal cancer. Journal of Experimental & Clinical Cancer Research: CR 38, 14.CrossRefGoogle ScholarPubMed
Lu, P et al. (2019) Fusobacterium nucleatum prevents apoptosis in colorectal cancer cells via the ANO1 pathway. Cancer Management and Research 11, 90579066.CrossRefGoogle ScholarPubMed
Liang, M et al. (2022) Fusobacterium nucleatum induces MDSCs enrichment via activation the NLRP3 inflammosome in ESCC cells, leading to cisplatin resistance. Annals of Medicine 54, 9891003.CrossRefGoogle ScholarPubMed
Silver, DP et al. (2010) Efficacy of neoadjuvant cisplatin in triple-negative breast cancer. Journal of Clinical Oncology 28, 11451153.CrossRefGoogle ScholarPubMed
Yamamura, K et al. (2019) Intratumoral Fusobacterium nucleatum levels predict therapeutic response to neoadjuvant chemotherapy in esophageal squamous cell carcinoma. Clinical Cancer Research 25, 61706179.CrossRefGoogle ScholarPubMed
Wang, WY et al. (2022) Comparison between diagnostic performance of intestinal Fusobacterium nucleatum, Bacteroides fragilis and Escherichia coli in 5-fluorouracil resistance to colorectal cancer: a metaanalysis. Cancer Treatment and Research Communications 32, 100536.CrossRefGoogle ScholarPubMed
Serna, G et al. (2020) Fusobacterium nucleatum persistence and risk of recurrence after preoperative treatment in locally advanced rectal cancer. Annals of Oncology 31, 13661375.CrossRefGoogle ScholarPubMed
Dong, J et al. (2021) Oral microbiota affects the efficacy and prognosis of radiotherapy for colorectal cancer in mouse models. Cell Reports 37, 109886.CrossRefGoogle ScholarPubMed
Topalian, SL, Drake, CG and Pardoll, DM (2015) Immune checkpoint blockade: a common denominator approach to cancer therapy. Cancer Cell 27, 450461.CrossRefGoogle ScholarPubMed
Ahmadzadeh, M et al. (2009) Tumor antigen-specific CD8 T cells infiltrating the tumor express high levels of PD-1 and are functionally impaired. Blood 114, 15371544.CrossRefGoogle ScholarPubMed
Cardoso, F et al. (2018) 4th ESO-ESMO international consensus guidelines for advanced breast cancer (ABC 4)dagger. Annals of Oncology 29, 16341657.CrossRefGoogle Scholar
Solinas, C et al. (2017) Targeting immune checkpoints in breast cancer: an update of early results. ESMO Open 2, e000255.CrossRefGoogle ScholarPubMed
Parkes, EE et al. (2021) The clinical and molecular significance associated with STING signaling in breast cancer. NPJ Breast Cancer 7, 81.CrossRefGoogle ScholarPubMed
Polonia, A et al. (2017) Prognostic value of stromal tumour infiltrating lymphocytes and programmed cell death-ligand 1 expression in breast cancer. Journal of Clinical Pathology 70, 860867.CrossRefGoogle ScholarPubMed
Humphries, MP et al. (2018) Automated tumour recognition and digital pathology scoring unravels new role for PD-L1 in predicting good outcome in ER-/HER2 + breast cancer. Journal of Oncology 2018, 2937012.CrossRefGoogle ScholarPubMed
Bertucci, F and Goncalves, A (2017) Immunotherapy in breast cancer: the emerging role of PD-1 and PD-L1. Current Oncology Reports 19, 64.CrossRefGoogle ScholarPubMed
Heimes, AS and Schmidt, M (2019) Atezolizumab for the treatment of triple-negative breast cancer. Expert Opinion on Investigational Drugs 28, 15.CrossRefGoogle ScholarPubMed
Adams, S et al. (2019) Pembrolizumab monotherapy for previously untreated, PD-L1–positive, metastatic triple-negative breast cancer: cohort B of the phase II KEYNOTE-086 study. Annals of Oncology 30, 405411.CrossRefGoogle ScholarPubMed
Kwapisz, D (2021) Pembrolizumab and atezolizumab in triple-negative breast cancer. Cancer Immunology Immunotherapy 70, 607617.CrossRefGoogle ScholarPubMed
Schmid, P et al. (2020) Pembrolizumab for early triple-negative breast cancer. New England Journal of Medicine 382, 810821.CrossRefGoogle ScholarPubMed
Zacharakis, N et al. (2022) Breast cancers are immunogenic: immunologic analyses and a phase II pilot clinical trial using mutation-reactive autologous lymphocytes. Journal of Clinical Oncology 40, 17411754.CrossRefGoogle Scholar
Gao, Y et al. (2021) Fusobacterium nucleatum enhances the efficacy of PD-L1 blockade in colorectal cancer. Signal Transduction and Targeted Therapy 6, 398.CrossRefGoogle ScholarPubMed
Trujillo, JA et al. (2018) T cell-inflamed versus non-T cell-inflamed tumors: a conceptual framework for cancer immunotherapy drug development and combination therapy selection. Cancer Immunology Research 6, 9901000.CrossRefGoogle ScholarPubMed
Chu, S et al. (2022) Airway Fusobacterium is associated with poor response to immunotherapy in lung cancer. OncoTargets and Therapy 15, 201213.CrossRefGoogle ScholarPubMed
Huang, Q, Peng, Y and Xie, F (2018) Fecal Fusobacterium nucleatum for detecting colorectal cancer: a systematic review and meta-analysis. International Journal of Biological Markers 33, 345352.CrossRefGoogle Scholar
Datorre, JG et al. (2022) Accuracy and clinical relevance of intra-tumoral Fusobacterium nucleatum detection in formalin-fixed paraffin-embedded (FFPE) tissue by droplet digital PCR (ddPCR) in colorectal cancer. Diagnostics 12, 114.CrossRefGoogle ScholarPubMed
de Carvalho, AC et al. (2019) Microbiota profile and impact of Fusobacterium nucleatum in colorectal cancer patients of Barretos Cancer Hospital. Frontiers in Oncology 9, 813.CrossRefGoogle ScholarPubMed
Tunsjo, HS et al. (2019) Detection of Fusobacterium nucleatum in stool and colonic tissues from Norwegian colorectal cancer patients. European Journal of Clinical Microbiology & Infectious Diseases 38, 13671376.CrossRefGoogle ScholarPubMed
Yamamura, K et al. (2017) Fusobacterium nucleatum in gastroenterological cancer: evaluation of measurement methods using quantitative polymerase chain reaction and a literature review. Oncology Letters 14, 63736378.Google ScholarPubMed
de Goffau, MC et al. (2018) Recognizing the reagent microbiome. Nature Microbiology 3, 851853.CrossRefGoogle ScholarPubMed
Walker, SP et al. (2020) Non-specific amplification of human DNA is a major challenge for 16S rRNA gene sequence analysis. Scientific Reports 10, 16356.CrossRefGoogle Scholar
Walker, SP, Tangney, M and Claesson, MJ (2020) Sequence-based characterization of intratumoral bacteria – a guide to best practice. Frontiers in Oncology 10, 179.CrossRefGoogle ScholarPubMed
Chen, WD et al. (2022) Salivary Fusobacterium nucleatum serves as a potential diagnostic biomarker for gastric cancer. World Journal of Gastroenterology 28, 41204132.CrossRefGoogle ScholarPubMed
Gopalakrishnan, V et al. (2018) Gut microbiome modulates response to anti-PD-1 immunotherapy in melanoma patients. Science 359, 97103.CrossRefGoogle ScholarPubMed
Routy, B et al. (2018) Gut microbiome influences efficacy of PD-1-based immunotherapy against epithelial tumors. Science 359, 9197.CrossRefGoogle ScholarPubMed
Lehouritis, P et al. (2015) Local bacteria affect the efficacy of chemotherapeutic drugs. Scientific Reports 5, 14554.CrossRefGoogle ScholarPubMed
Kabwe, M et al. (2019) Genomic, morphological and functional characterisation of novel bacteriophage FNU1 capable of disrupting Fusobacterium nucleatum biofilms. Scientific Reports 9, 9107.CrossRefGoogle ScholarPubMed
Li, X et al. (2022) Gut microbiome in modulating immune checkpoint inhibitors. EBioMedicine 82, 104163.CrossRefGoogle ScholarPubMed
Tarantino, P et al. (2022) Immunotherapy for early triple negative breast cancer: research agenda for the next decade. NPJ Breast Cancer 8, 23.CrossRefGoogle ScholarPubMed
Figure 0

Figure 1. The microbiome is a key regulator of the tumour microenvironment (TME). Secreted factors and ‘immunomodulatory’ factors produced by bacteria can activate damage sensors on immune cells, for example, outer membrane vesicles which contain proinflammatory molecules such as lipopolysaccharide (LPS) on Gram-negative bacteria which stimulates Toll-like receptor (TLR)-4 signalling in immune cells. This activation results in the expression of a range of chemokines and cytokines, which further influence the recruitment and behaviour of immune cells within the TME and can lead to a state of chronic inflammation. Cells present in the TME can also produce growth factors and serine proteases which induce tumour progression. Furthermore, bacteria secrete metabolites such as short chain fatty acids (SCFAs) which can interact with the TME to reshape it, and/or cause genomic instability within the cells. LPS, lipopolysaccharide; SCFA, short-chain fatty acid; ROS, reactive oxygen species; TLR, Toll-like receptor; NLR, Nod-like receptor. Figure created with BioRender.

Figure 1

Figure 2. Known oncogenic pathways modulated by Fusobacterium nucleatum. F. nucleatum (shown in blue) binds to tumour cells via interaction of its Fap2 protein with D-galactose-β(1–3)-N-acetyl-D-galactosamine (Gal-GalNAc) or by FadA interacting with E-cadherin, which is enhanced by Annexin A1 (ANXA1), enabling attachment and invasion of tumour cells. F. nucleatum also secretes outer membrane vesicles (OMVs) and lipopolysaccharide (LPS) which interact with the Toll-like receptors (TLRs) to initiate downstream signalling pathways that mediate the release of inflammatory cytokines and transcription of miR-21 which is known to regulate the activity of the oncoprotein RASA1. The E-cadherin and TLR4 signalling induced by F. nucleatum binding stimulates β-catenin accumulation in the cytoplasm and its subsequent translocation to the nucleus where it upregulates transcription of oncogenes including c-MYC and Cyclin D1. Furthermore, F. nucleatum is able to aid metastasis through OMV-mediated degradation of E. cadherin, NF-κB mediated increased expression of keratin 7 (KRT7), and via induction of the inflammatory cytokines IL-8 and CXCL1. Figure created with BioRender.

Figure 2

Figure 3. Known pathways induced by F. nucleatum binding that result in increased interleukin-8 (IL-8) secretion. (a) F. nucleatum infection in Caco-2 colorectal cancer cells impaired autophagic flux, which enhanced the production of TNF-α, IL-1β and IL-8 via the increase in reactive oxygen species (ROS). (b) F. nucleatum binding via its FadA adhesin to the sugar D-galactose-β(1–3)-N-acetyl-D-galactosamine (Gal-GalNAc) on colorectal cancer cells enables invasion, which further stimulates the release of IL-8 and CXCL1. (c) Outer membrane vesicles and the porin FomA secreted by F. nucleatum stimulate Toll-like receptors (TLRs) 2 and 4 on colonic epithelial cells, inducing NF-κB signalling that results in increased IL-8 secretion. (d) F. nucleatum's FadA adhesin binds to E-cadherin, activating β-catenin signalling in CRC cells, resulting in increased expression of pro-inflammatory cytokines, including IL-8. Figure created with BioRender.

Figure 3

Table 1. The effect of F. nucleatum on immune cells from different studies