Exploring the microbiota to better understand gastrointestinal cancers physiology

The role of intermittent fasting and the ketogenic diet in cancer disease: can they replace the Mediterranean diet?

The prevalence of cancer is rising globally, and it is the second leading cause of death. Nutrition has an important influence on the risk of developing cancer. Moreover, changes in the gut microbiota are connected to the risk of developing cancer and are critical for sustaining immunity. Various studies have shown that intermittent fasting, ketogenic diet, and the Mediterranean diet are effective therapies in changing the intestinal microbiota, the prevention of cancer, and the improvement of tolerance to treatment in cancer patients. Although there is not enough evidence to show that the ketogenic diet is effective in changing the intestinal microbiota in a manner that could prevent cancer, intermittent fasting and the Mediterranean diet could positively affect composition of intestinal microbiota against cancer. In addition, the ketogenic diet, intermittent fasting, and the Mediterranean diet have the potential to stimulate anticarcinogenic pathways, and they might increase cancer patients' quality of life according to scientific evidence. In this review, we represent and argue recent scientific data on relationship between intermittent fasting, the ketogenic diet, and the Mediterranean diet, intestinal microbiota, cancer prevention and cancer treatment.

Microbiota as a New Target in Cancer Pathogenesis and Treatment

The microbial ecosystem of humans is an integral part of human health and disease. A significant percentage of tumors worldwide are thought to be microbially induced. The relationship between cancer and microbes is complex. In this article review, we aim to give an overview of human microbiota and its role in carcinogenesis, emphasize the relation between microbiota and cancer immunity, and highlight its role in the future of cancer therapy. The term microbiota refers to the collection of microorganisms that are located in an individual, whereas the total genome of these microorganisms is referred to as the microbiome. The microbiota in humans has many physiological functions. The microbiota within the gut lumen has a profound effect on the local and systemic immune system. The immune system can change the gut microbiota. Microbiota may induce carcinogenesis by several mechanisms. It also affects tumor progression. Thus, microbiota modulation may aid in the prevention and treatment of cancer. Intentionally introducing microorganisms into the oncological patient is assumed to mobilize the immune system to become able to, at least, limit the development of cancer. Microbes are used as vectors which are carriers of particular antineoplastic agents that reduce the side effects of chemotherapy. Inflammation and tumor microenvironment play an essential role in promoting chemo-resistance. There is now considerable evidence, both in humans as well as in laboratory animals, that the commensal microbiota has important effects on carcinogenesis, tumor growth, and therapy response.

The role of microbiota in the development and treatment of gastric cancer

The stomach was once considered a sterile organ until the discovery of Helicobacter pylori (HP). With the application of high-throughput sequencing technology and macrogenomics, researchers have identified fungi and fivemajor bacterial phyla within the stomachs of healthy individuals. These microbial communities exert regulatory influence over various physiological functions, including energy metabolism and immune responses. HP is a well-recognized risk factor for gastric cancer, significantly altering the stomach's native microecology. Currently, numerous studies are centered on the mechanisms by which HP contributes to gastric cancer development, primarily involving the CagA oncoprotein. However, aside from exogenous infections such as HP and EBV, certain endogenous dysbiosis can also lead to gastric cancer through multiple mechanisms. Additionally, gut microbiota and its metabolites significantly impact the development of gastric cancer. The role of microbial therapies, including diet, phages, probiotics and fecal microbiota transplantation, in treating gastric cancer should not be underestimated. This review aims to study the mechanisms involved in the roles of exogenous pathogen infection and endogenous microbiota dysbiosis in the development of gastric cancer. Also, we describe the application of microbiota therapy in the treatment and prognosis of gastric cancer.

Cell-free Lactiplantibacillus plantarum OC01 supernatant suppresses IL-6-induced proliferation and invasion of human colorectal cancer cells: Effect on β-Catenin degradation and induction of autophagy

Background and aim

Gut microbiota is considered as a complex organ of human body. The interaction between the host and microbiota is dynamic and controlled by a huge number of factors, such as lifestyle, geography, pharmaceuticals, diet, and stress. The breakdown of this relationship could change microbiota composition favoring the onset of several diseases, including cancer. Metabolites released by microbiota bacterial strains have been reported to elicit protective effects on the mucosa that could contrast cancer development and progression. Here, we tested the ability of specific probiotic strain Lactiplantibacillus plantarum OC01-derived metabolites (NCIMB 30624) to contrast the malignant features of colorectal cancer (CRC) cells.

Experimental procedure

The study was performed on two cell lines, HCT116 and HT29, cultured in 2D and 3D, and focused on the hallmarks of cell proliferation and migration.

Results and conclusion

Probiotic metabolites reduced cell proliferation both in 2D and 3D-spheroid cultures, the latter model mimicking the growth in vivo. The bacterial metabolites also contrasted the pro-growth and pro-migratory activity of inteurleukin-6 (IL-6), an inflammatory cytokine abundantly found in the tumor microenvironment of CRC. These effects were associated with inhibition of the ERK and of the mTOR/p70S6k pathways and with the inhibition of the E-to N-Cadherin switch. In a parallel study, we found that sodium butyrate (a representative of the main probiotic metabolites) induced autophagy and β-Catenin degradation, which is consistent with the growth inhibitory activity. The present data indicate that the metabolites of Lactiplantibacillus plantarum OC01 (NCIMB 30624) elicits anti-tumor effect and support its possible inclusion as adjuvant therapy of CRC for limiting cancer growth and progression.

Diet-gut microbial interactions influence cancer immunotherapy

The gut microbiome is involved in the absorption and metabolism of host nutrients and modulates the immune response, affecting the efficacy of immunotherapy for cancer. In patients receiving immunotherapy, appropriate modifications of gut microbiota are thought to improve therapeutic response. Of all the factors that influence the gut microbiota, diet is the most influential and modifiable. Healthy dietary patterns as well as some specific dietary components can help the growth of beneficial microbiota in the gut, thereby protecting against cancers and promoting human health. A growing number of researches have confirmed the positive effects of a diet-gut microbiota approach as an adjuvant therapy for cancer, but controversy remains. Here, we summarize the interactions between diet and gut microbes based on previous studies, and discuss the role of gut microbiota-based dietary strategies in tumor immunotherapy, with the potential mechanisms of actions also intensively discussed.

Butyrate Inhibits Colorectal Cancer Cell Proliferation through Autophagy Degradation of β-Catenin Regardless of APC and β-Catenin Mutational Status

Colorectal cancer (CRC) pathogenesis is mainly driven by alterations in WNT signaling, which results in altered transcriptional activity of β-Catenin. Mutations in APC (Adenomatous Polyposis Coli) are reflected in β-Catenin hyperactivation and loss of proliferation control. Certain intestinal bacteria metabolites have shown the ability to limit CRC cell proliferation and CRC pathogenesis. Here, we investigated the molecular mechanism underlying the anti-proliferative activity of butyrate, a microbiota-derived short chain fatty acid, in two CRC cell lines, namely HCT116 and SW620, which bear a mutation in β-Catenin and APC, respectively. In particular, we focused on autophagy, a lysosome-dependent degradation pathway, which was shown to control intestinal tissue homeostasis. Butyrate reduced CRC cell proliferation, as witnessed by the downregulation of proliferation markers. TCGA bioinformatic transcriptomic analysis of CTNNB1 (β-Catenin) gene correlation in CRC patients showed that β-Catenin negatively correlates with the autophagy gene ATG4D. In CRC cells, regardless of the mutational state of APC or β-Catenin genes, butyrate caused the autophagy-mediated degradation of β-Catenin; thus, preventing its transcriptional activity. Autophagy gene silencing restored β-Catenin levels, allowing it to translocate into the nucleus to promote the expression of downstream genes associated with cancer cell proliferation. CRC-affected patients show driver mutations in the WNT pathway; thus, targeting its crucial effector may be a promising therapeutic strategy in CRC treatment; for instance, by using ad hoc probiotics that stimulate autophagy.

A proposal for the reference intervals of the Italian microbiota "scaffold" in healthy adults

Numerous factors, ranging from genetics, age, lifestyle, and dietary habits to local environments, contribute to the heterogeneity of the microbiota in humans. Understanding the variability of a “healthy microbiota” is a major challenge in scientific research. The gut microbiota profiles of 148 healthy Italian volunteers were examined by 16S rRNA gene sequencing to determine the range and diversity of taxonomic compositions in the gut microbiota of healthy populations. Possible driving factors were evaluated through a detailed anamnestic questionnaire. Microbiota reference intervals were also calculated. A “scaffold” of a healthy Italian gut microbiota composition was identified. Differences in relative quantitative ratios of microbiota composition were detected in two clusters: a bigger cluster (C₂), which included 124 subjects, was characterized by more people from the northern Italian regions, who habitually practised more physical activity and with fewer dietary restrictions. Species richness and diversity were significantly higher in this cluster (C₂) than in the other one (C₁) (C₁: 146.67 ± 43.67; C₂: 198.17 ± 48.47; F = 23.40; P < 0.001 and C₁: 16.88 ± 8.66; C₂: 35.01 ± 13.40; F = 40.50; P < 0.001, respectively). The main contribution of the present study was the identification of the existence of a primary healthy microbiological framework that is only marginally affected by variations. Taken together, our data help to contextualize studies on population-specific variations, including marginal aspects, in human microbiota composition. Such variations must be related to the primary framework of a healthy microbiota and providing this perspective could help scientists to better design experimental plans and develop strategies for precision tailored microbiota modulation.

Role of the microbiome in systemic therapy for pancreatic ductal adenocarcinoma (Review)

A large body of evidence has revealed that the microbiome serves a role in all aspects of cancer, particularly cancer treatment. To date, studies investigating the relationship between the microbiome and systemic therapy for pancreatic ductal adenocarcinoma (PDAC) are lacking. PDAC is a high‑mortality malignancy (5‑year survival rate; <9% for all stages). Systemic therapy is one of the most important treatment choices for all patients; however, resistance or toxicity can affect its efficacy. Studies have supported the hypothesis that the microbiome is closely associated with the response to systemic therapy in PDAC, including the induction of drug resistance, or toxicity and therapy‑related changes in microbiota composition. The present review comprehensively summarized the role of the microbiome in systemic therapy for PDAC and the associated molecular mechanisms in an attempt to provide a novel direction for the improvement of treatment response and proposed potential directions for in‑depth research.

Bacterial Extracellular Vesicles in Gastrointestinal Tract Cancer: An Unexplored Territory

Bacterial extracellular vesicles are membrane-enclosed, lipid bi-layer nanostructures that carry different classes of biomolecules, such as nucleic acids, lipids, proteins, and diverse types of small molecular metabolites, as their cargo. Almost all of the bacteria in the gut secrete extracellular vesicles to assist them in competition, survival, material exchange, host immune modulation, infection, and invasion. The role of gut microbiota in the development, progression, and pathogenesis of gastrointestinal tract (GIT) cancer has been well documented. However, the possible involvement of bacterial extracellular vesicles (bEVs) in GIT cancer pathophysiology has not been given due attention. Studies have illustrated the ability of bEVs to cross physiological barriers, selectively accumulate near tumor cells, and possibly alter the tumor microenvironment (TME). A systematic search of original published works related to bacterial extracellular vesicles on gastrointestinal cancer was performed for this review. The current systemic review outlines the possible impact of gut microbiota derived bEVs in GIT cancer in light of present-day understanding. The necessity of using advanced sequencing technologies, such as genetic, proteomic, and metabolomic investigation methodologies, to facilitate an understanding of the interrelationship between cancer-associated bacterial vesicles and gastrointestinal cancer is also emphasized. We further discuss the clinical and pharmaceutical potential of bEVs, along with future efforts needed to understand the mechanism of interaction of bEVs in GIT cancer pathogenesis.

From microbiota toward gastro-enteropancreatic neuroendocrine neoplasms: Are we on the highway to hell?

Gut microbiota is represented by different microorganisms that colonize the intestinal tract, mostly the large intestine, such as bacteria, fungi, archaea and viruses. The gut microbial balance has a key role in several functions. It modulates the host's metabolism, maintains the gut barrier integrity, participates in the xenobiotics and drug metabolism, and acts as protection against gastro-intestinal pathogens through the host's immune system modulation. The impaired gut microbiota, called dysbiosis, may be the result of an imbalance in this equilibrium and is linked with different diseases, including cancer. While most of the studies have focused on the association between microbiota and gastrointestinal adenocarcinomas, very little is known about gastroenteropancreatic (GEP) neuroendocrine neoplasms (NENs). In this review, we provide an overview concerning the complex interplay between gut microbiota and GEP NENs, focusing on the potential role in tumorigenesis and progression in these tumors.

Chemotherapy-Induced Intestinal Microbiota Dysbiosis Impairs Mucosal Homeostasis by Modulating Toll-like Receptor Signaling Pathways

Chemotherapy-induced intestinal mucositis, a painful debilitating condition affecting up to 40–100% of patients undergoing chemotherapy, can reduce the patients’ quality of life, add health care costs and even postpone cancer treatment. In recent years, the relationships between intestinal microbiota dysbiosis and mucositis have drawn much attention in mucositis research. Chemotherapy can shape intestinal microbiota, which, in turn, can aggravate the mucositis through toll-like receptor (TLR) signaling pathways, leading to an increased expression of inflammatory mediators and elevated epithelial cell apoptosis but decreased epithelial cell differentiation and mucosal regeneration. This review summarizes relevant studies related to the relationships of mucositis with chemotherapy regimens, microbiota, TLRs, inflammatory mediators, and intestinal homeostasis, aiming to explore how gut microbiota affects the pathogenesis of mucositis and provides potential new strategies for mucositis alleviation and treatment and development of new therapies.

The Microbiome as a Potential Target for Therapeutic Manipulation in Pancreatic Cancer

Simple Summary

Pancreatic cancer is one of the most lethal cancers. It is a difficult cancer to treat, and the complexity surrounding the pancreatic tumour is one of the contributing factors. The microbiome is the collection of microorganisms within an environment and its genetic material. They reside on body surfaces and most abundantly within the human gut in symbiotic balance with their human host. Disturbance in the balance can lead to many diseases, including cancers. Significant advances have been made in cancer treatment since the introduction of immunotherapy, and the microbiome may play a part in the outcome and survival of patients with cancer, especially those treated with immunotherapy. Immunotherapy use in pancreatic cancer remains challenging. This review will focus on the potential interaction of the microbiome with pancreas cancer and how this could be manipulated.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers and is projected to be the second most common cause of cancer-related death by 2030, with an overall 5-year survival rate between 7% and 9%. Despite recent advances in surgical, chemotherapy, and radiotherapy techniques, the outcome for patients with PDAC remains poor. Poor prognosis is multifactorial, including the likelihood of sub-clinical metastatic disease at presentation, late-stage at presentation, absence of early and reliable diagnostic biomarkers, and complex biology surrounding the extensive desmoplastic PDAC tumour micro-environment. Microbiota refers to all the microorganisms found in an environment, whereas microbiome is the collection of microbiota and their genome within an environment. These organisms reside on body surfaces and within mucosal layers, but are most abundantly found within the gut. The commensal microbiome resides in symbiosis in healthy individuals and contributes to nutritive, metabolic and immune-modulation to maintain normal health. Dysbiosis is the perturbation of the microbiome that can lead to a diseased state, including inflammatory bowel conditions and aetiology of cancer, such as colorectal and PDAC. Microbes have been linked to approximately 10% to 20% of human cancers, and they can induce carcinogenesis by affecting a number of the cancer hallmarks, such as promoting inflammation, avoiding immune destruction, and microbial metabolites can deregulate host genome stability preceding cancer development. Significant advances have been made in cancer treatment since the advent of immunotherapy. The microbiome signature has been linked to response to immunotherapy and survival in many solid tumours. However, progress with immunotherapy in PDAC has been challenging. Therefore, this review will focus on the available published evidence of the microbiome association with PDAC and explore its potential as a target for therapeutic manipulation.

Research progress on gut microbiota in patients with gastric cancer, esophageal cancer, and small intestine cancer

The pathogenesis of gut microbiota in humans can be indicated due to the wide application of techniques, such as 16S rRNA sequencing. Presently, several studies have found a significant difference in fecal flora between normal individuals and patients with gastric cancer. Although clinical research on the feedback mechanism of gastric flora and gut microbiota is lacking, clarifying the relationship between gut microbiota and the characteristics of cancer is significant for the early diagnosis of gastric cancer. This study was conducted to review the results of several studies in the past 5 years and analyze the intestinal bacteria in patients with gastric cancer and compare them with those in patients with esophageal and small intestine cancers. It was found that the gut microbiota in patients with gastric cancer was similar to that in patients with esophageal cancer. However, making an analysis and comparing the gut microbiota in patients with small intestine and gastric cancers was impossible due to the low incidence of small intestinal cancer. Our review summarized the research progress on using the gut microbiota for early screening for gastric cancer, and the results of this study will provide a further direction in this field. KEY POINTS: • We reviewed several relative mechanisms of the gut microbiota related to gastric cancer. • The gut microbiota in gastric, esophageal, and small intestine cancers are significantly different in types and quantity, and we have provided some tips for further research. • A prospective review of sequencing methods and study results on the gut microbiota in gastric, esophageal, and small intestine cancers was described.

The role of the microbiome in drug resistance in gastrointestinal cancers

Introduction: The microbiota is recognized for its impact on both human health and disease. The human microbiota is made up of trillions of cells, including bacteria, viruses, and fungi. The largest population of microbes reside in the gut, prompting research for better understanding of the impact of gastrointestinal microbiota in different diseases. Evidence from numerous studies has pointed out the role of commensal microbes as key determinants of cancer pathogenesis. Moreover, gut microbiota may play an important role in chemoresistance; consequently, this knowledge might be important for novel strategies to improve anticancer treatment efficacy.Areas covered: We describe the role of microbiota in different gastrointestinal cancer types (esophageal, gastric, colorectal, hepatocellular and pancreatic-biliary tract cancers). Moreover, we analyzed the impact of the microbiota on resistance to anticancer therapies, and, lastly, we focused on possibilities of microbiota modulation to enhance anticancer therapy efficacy.Expert opinion: Increasing evidence shows that gut microbiota might influence resistance to anticancer treatment, including conventional chemotherapy, immunotherapy, radiotherapy, and surgery. Therefore, a better knowledge of gut microbiota and its interactions with anticancer drugs will enable us to develop novel anticancer treatment strategies and subsequently improve the cancer patients' outcome.

Pancreatic Cancer, Gut Microbiota, and Therapeutic Efficacy

Pancreatic cancer remains one of the leading causes of cancer-related death worldwide and has a poor prognosis. Current treatment relies on surgical resection and adjuvant therapies. The gut microbiota plays important roles in metabolism and immunomodulation. Accumulating evidence has implied that the gut microbiota is involved in the metabolism of chemotherapeutic drugs and the tumor microenvironment (TME), which could affect the efficacy of both conventional chemotherapy and immunotherapy for pancreatic cancer. Herein, we comprehensively reviewed the history and highlights of the interactions among pancreatic cancer, the gut microbiota and therapeutic efficacy and showed the promising future of manipulating the gut microbiota to improve clinical outcomes of pancreatic cancer.

Gut Microbiota Profiles Differ among Individuals Depending on Their Region of Origin: An Italian Pilot Study

Background and aims: Microbiota heterogeneity among humans is mainly due to genetic background, age, dietary habits, lifestyle and local environments. In this study we investigated whether the gut microbiota profile of Italian healthy volunteers could differ based on their geographical origin. Materials and Methods: 16S rRNA gene sequencing was employed to analyze the gut microbiota of 31 healthy volunteers from three different Italian regions: Apulia (South), Lazio (Center) and Lombardy (North). Results: Differences in microbiota composition were detected when the study participants were grouped by their region of origin and when they were classified based on age classes (p-values < 0.05). Also species richness was significantly different both according to Italian Regions (median richness: 177.8 vs. 140.7 vs. 168.0 in Apulia, Lazio and Lombardy; p < 0.001) and according to age classes (median richness: 140.1 vs. 177.8 vs. 160.0 in subjects < 32, 32–41 and > 41 years; p < 0.001), whereas the Shannon index and beta diversity did not change. Conclusions: This study identified differences in the gut microbiota composition and richness among individuals with the same ethnicity coming from three different Italian regions. Our results underline the importance of studies on population-specific variations in human microbiota composition leading to geographically tailored approaches to microbiota engineering.

The impact of tumor and gut microbiotas on cancer therapy: Beneficial or detrimental?

Cancer is a globally challenging health problem threatening mankind. Despite therapeutic advances in dealing with this malignancy, heterogeneous response and resistance to chemotherapeutic agents remain the hallmarks of cancer therapy. On the other hand, the involvement of the microbiota in affecting human health is well defined. An ever-growing body of evidence implicates the potential link between the microbiome and the efficacy of cancer therapies. Gut microbiota can modulate the metabolism of drugs in a number of ways. The presence of bacteria within the tumor environment can also impact the responses to cancer therapies; changing the chemical structure of chemotherapeutic drugs, affecting their activity, and local concentration. However, the underlying mechanisms by which gut and tumor microbial communities affect the response to cancer therapy are poorly understood and deciphering these mechanisms is of paramount importance. This review provides an overview of how gut and tumor microbiota might affect the efficacy of chemotherapy, radiotherapy, and immunotherapy and alleviate the adverse side effects of these therapies for the development of personalized and effective anticancer therapy.

Body site-dependent variations of microbiota in pancreatic cancer pathophysiology

Lack of specific symptoms and reliable biomarkers, along with aggressive nature and resistance to therapies makes pancreatic cancer (PC) one of the leading causes of death from cancer worldwide. The search for new diagnostic, prognostic, predictive, and therapeutic tools that could improve clinical outcomes of patients has led, in recent years, to the investigation of potential roles for the microbiota in the pathogenesis of this disease. The human microbiota encompasses trillions of microorganisms residing within several body tissues and organs, where they provide beneficial functions for host homeostasis and health. Derangements of the microbial ecology in different anatomic districts have been described in PC, as in many other diseases, both in patients and in animal models. In detail, infection from the gastric pathogen Helicobacter pylori and changes in composition and diversity of oral, intestinal, and pancreatic microbiota have been found to associate with PC. Future research should assess how to potentially exploit such differences in microbiota composition as diagnostic, prognostic, or predictive biomarkers, and as targets for therapeutic interventions, in the hope of improving the dismal prognosis of this insidious cancer.

Impact of Different Types of Diet on Gut Microbiota Profiles and Cancer Prevention and Treatment

: Diet is frequently considered as a food regimen focused on weight loss, while it is actually the sum of food consumed by the organism. Western diets, modern lifestyle, sedentary behaviors, smoking habits, and drug consumption have led to a significant reduction of gut microbial diversity, which is linked to many non-communicable diseases (NCDs). The latter kill 40 million people each year, equivalent to more than 70% of all deaths globally. Among NCDs, tumors play a major role, being responsible for 29% of deaths from NCDs. A link between diet, microbiota, and cancer prevention and treatment has recently been unveiled, underlining the importance of a new food culture based on limiting dietary surplus and on preferring healthier foods. Here, we review the effects of some of the most popular "cancer-specific" diets on microbiota composition and their potential impact on cancer prevention and treatment.

Inflammation and Pancreatic Cancer: Focus on Metabolism, Cytokines, and Immunity. Int J Mol Sci. 2019;20. [PMID: 30764482 PMCID: PMC6387440 DOI: 10.3390/ijms20030676]

Systemic and local chronic inflammation might enhance the risk of pancreatic ductal adenocarcinoma (PDAC), and PDAC-associated inflammatory infiltrate in the tumor microenvironment concurs in enhancing tumor growth and metastasis. Inflammation is closely correlated with immunity, the same immune cell populations contributing to both inflammation and immune response. In the PDAC microenvironment, the inflammatory cell infiltrate is unbalanced towards an immunosuppressive phenotype, with a prevalence of myeloid derived suppressor cells (MDSC), M2 polarized macrophages, and T_reg, over M1 macrophages, dendritic cells, and effector CD4⁺ and CD8⁺ T lymphocytes. The dynamic and continuously evolving cross-talk between inflammatory and cancer cells might be direct and contact-dependent, but it is mainly mediated by soluble and exosomes-carried cytokines. Among these, tumor necrosis factor alpha (TNFα) plays a relevant role in enhancing cancer risk, cancer growth, and cancer-associated cachexia. In this review, we describe the inflammatory cell types, the cytokines, and the mechanisms underlying PDAC risk, growth, and progression, with particular attention on TNFα, also in the light of the potential risks or benefits associated with anti-TNFα treatments.

Pembrolizumab for the treatment of gastric cancer

INTRODUCTION

Gastric cancer is one of a few gastrointestinal malignancies in which immunotherapy has shown meaningful activity. Pembrolizumab is the first and only immune checkpoint inhibitor to be FDA-approved in gastric cancer. Areas Covered: This review summarizes the current and emerging clinical evidence for immune checkpoint inhibitors in advanced and metastatic gastric cancer, with a focus on pembrolizumab. Expert Commentary: Pembrolizumab has shown impressive activity in the third-line treatment of locally advanced and metastatic gastric cancer. It is currently being studied as upfront therapy in combination with chemotherapy. The emerging understanding of the molecular alterations and tumor immune microenvironment as predictors of immunotherapy response in gastric cancer are discussed. The impact of gastric mucosal dysbiosis on gastric carcinogenesis and the modulation of immunotherapy response by the gut microbiome are also reviewed.

Pharmacomicrobiomics: exploiting the drug-microbiota interactions in anticancer therapies

Cancer is a major health burden worldwide, and despite continuous advances in medical therapies, resistance to standard drugs and adverse effects still represent an important cause of therapeutic failure. There is a growing evidence that gut bacteria can affect the response to chemo- and immunotherapeutic drugs by modulating either efficacy or toxicity. Moreover, intratumor bacteria have been shown to modulate chemotherapy response. At the same time, anticancer treatments themselves significantly affect the microbiota composition, thus disrupting homeostasis and exacerbating discomfort to the patient. Here, we review the existing knowledge concerning the role of the microbiota in mediating chemo- and immunotherapy efficacy and toxicity and the ability of these therapeutic options to trigger dysbiotic condition contributing to the severity of side effects. In addition, we discuss the use of probiotics, prebiotics, synbiotics, postbiotics, and antibiotics as emerging strategies for manipulating the microbiota in order to improve therapeutic outcome or at least ensure patients a better quality of life all along of anticancer treatments.