Human gut microbiota play an essential role in both healthy and diseased states of humans. In the past decade, the interactions between microorganisms and tumors have attracted much attention in the efforts to understand various features of the complex microbial communities, as well as the possible mechanisms through which the microbiota are involved in cancer prevention, carcinogenesis, and anti-cancer therapy. A large number of studies have indicated that microbial dysbiosis contributes to cancer susceptibility via multiple pathways. Further studies have suggested that the microbiota and their associated metabolites are not only closely related to carcinogenesis by inducing inflammation and immune dysregulation, which lead to genetic instability, but also interfere with the pharmacodynamics of anticancer agents. In this article, we mainly reviewed the influence of gut microbiota on cancers in the gastrointestinal (GI) tract (including esophageal, gastric, colorectal, liver, and pancreatic cancers) and the regulation of microbiota by diet, prebiotics, probiotics, synbiotics, antibiotics, or the Traditional Chinese Medicine. We also proposed some new strategies in the prevention and treatment of GI cancers that could be explored in the future. We hope that this review could provide a comprehensive overview of the studies on the interactions between the gut microbiota and GI cancers, which are likely to yield translational opportunities to reduce cancer morbidity and mortality by improving prevention, diagnosis, and treatment.

Cancer-associated fibroblasts (CAFs) play critical roles in cancer progression by regulating tumor cell proliferation, angiogenesis, and metastasis. Recent studies demonstrated that CAFs induce inhibitory immune cell infiltration and chemotherapy resistance in gastric cancer by activating the NF-κB signaling pathway to secrete IL6, IL8, and other inflammatory factors. Inhibition of the NF-κB signaling pathway in CAFs might be a potential therapeutic strategy in gastric cancer. However, how the NF-κB pathway is activated in CAFs remains unclear. We showed that mesenchymal stem cells (MSCs) differentiated into CAFs, induced by the exosomes derived from gastric cancer cells. During the process of differentiation from MSCs into CAFs, we showed that nuclear PKM2 expression was continuously upregulated and associated with NF-κB P65 acetylation, contributing to P65 nuclear retention in CAFs and constant transcription of IL-6, IL-8, and other inflammatory factors, thus promoting gastric cancer cell proliferation. We showed that NF-κB P65 acetylation was induced by P300. We showed that nuclear PKM2 was derived from exosomes of gastric cancer cell lines and the positive feedback loop induced by PKM2-P65 combination. It is also proved that P300 inhibitors can inhibit tumor proliferation in an AGS subcutaneous xenograft tumor model. Our study showed that gastric cancer cells influence the continuous activation of the NF-κB signaling pathway in CAFs by secreting gastric cancer exosomes containing PKM2, thus inducing abnormal metabolism and inflammation activation. This study provides a new therapeutic target for CAF normalization or deactivation strategies.

First‐line chemotherapy for advanced/metastatic human epidermal growth factor receptor 2 (HER2)‐negative gastric/gastroesophageal junction cancer (GC/GEJC) has poor median overall survival (OS; <1 year). We report efficacy and safety results from Chinese patients in the phase III global CheckMate 649 study of nivolumab plus chemotherapy vs chemotherapy for the first‐line treatment of GC/GEJC/esophageal adenocarcinoma (EAC). Chinese patients with previously untreated advanced or metastatic GC/GEJC/EAC were randomized to receive nivolumab (360 mg Q3W or 240 mg Q2W) plus chemotherapy (XELOX [capecitabine and oxaliplatin] Q3W or FOLFOX [oxaliplatin, leucovorin and 5‐fluorouracil] Q2W), nivolumab plus ipilimumab (not reported) or chemotherapy alone. OS, blinded independent central review‐assessed progression‐free survival (PFS), objective response rate (ORR), duration of response (DOR) and safety are reported. Of 1581 patients enrolled and randomized, 208 were Chinese. In these patients, nivolumab plus chemotherapy resulted in clinically meaningful improvement in median OS (14.3 vs 10.2 months; HR 0.61 [95% CI: 0.44‐0.85]), median PFS (8.3 vs 5.6 months; HR 0.57 [95% CI: 0.40‐0.80]), ORR (66% vs 45%) and median DOR (12.2 vs 5.6 months) vs chemotherapy, respectively. The safety profile was acceptable, with no new safety signals observed. Consistent with results from the global primary analysis of CheckMate 649, nivolumab plus chemotherapy demonstrated a clinically meaningful improvement in OS and PFS and higher response rate vs chemotherapy and an acceptable safety profile in Chinese patients. Nivolumab plus chemotherapy represents a new standard first‐line treatment for Chinese patients with non‐HER2‐positive advanced GC/GEJC/EAC.

Objective: The prognosis of advanced gastrointestinal cancer is poor. There are studies indicating that gut microbes might have the predictive ability to evaluate the outcome of cancer therapy, especially immunotherapy. There is limited evidence to date on the influence of microbes on chemotherapeutic response.Design: In total, 130 patients with advanced or metastatic esophageal (n=40), gastric (n=46), and colorectal cancer (n=44) were enrolled. We included 147 healthy people as controls and used 16S rRNA sequencing to analyze the fecal microbiota.Results: Significant differences in the abundance of fecal microbiota between patients with gastrointestinal cancer and controls were identified. The abundance of Bacteroides fragilis, Escherichia coli, Akkermansia muciniphila, Clostridium hathewayi, and Alistipes finegoldii were significantly increased in the patient group. Faecalibacterium prausnitzii, Roseburia faecis, Clostridium clostridioforme, Blautia producta, Bifidobacterium adolescent, and Butyricicoccus pullicaecorum taxa were significantly more abundant in the controls. The amount of R. faecis in non-responders (NR) was more likely to decrease significantly after chemotherapy, while the amount mostly increased in responders (R) (P=0.040). The optimal abundance variation of R. faecis may be a predictor for distinguishing patients with PD from those with non-PD in all patients with gastrointestinal cancer, with a sensitivity of 75.0% and a specificity of 93.9%.Conclusion: The gut microbiome of patients with esophageal cancer, gastric cancer, and colorectal cancer differs from those of healthy people. The abundance alteration of R. faecis in patients with GI cancer might be a predictor of chemotherapy efficacy.

The objective of this study was to predict the value of lymphocyte subsets in cancer progression. Peripheral blood was obtained from 327 untreated patients with cancer and 158 healthy volunteers. Levels of lymphocyte subsets were determined by flow cytometry. There were decreased levels of natural killer (NK) cells, CD8⁺ T cells, and naïve CD4⁺/CD4⁺ T cells in untreated patients with cancer compared to those in healthy controls. Inversely, there were elevated levels of the following T‐cell percentages in cancer patients compared to those in healthy controls: memory CD4⁺/CD4⁺, CD8⁺ T cells, HLA‐DR/CD8⁺, CD8⁺ CD38⁺/CD8⁺, and CD4⁺/CD8⁺. In addition, there are a decreasing trend in terms of CD4⁺ T‐cell counts and an increase CD8⁺ HLA‐DR/CD8⁺ T‐cell and CD8⁺ CD38⁺/CD8⁺ T‐cell percentages in the advanced stage. An increasing trend with advanced tumor stage and the percentages of CD8⁺ HLA‐DR/CD8⁺ T cells and CD8⁺ CD38⁺/CD8⁺ T cells was shown in this study. There are a negative correlation for CD4⁺ T‐cell counts and positive correlation for percentages of CD8⁺ HLA‐DR/CD8⁺ T cell and CD8⁺ CD38⁺/CD8⁺ T cells with the lymph node metastasis. In the presence of distant metastatic spread, we observed higher NK‐cell counts, CD8⁺ HLA‐DR/CD8⁺ T‐cell percentages, CD8⁺ CD38⁺/CD8⁺ T‐cell percentages, as well as lower CD4⁺ T‐cell counts than those in the absence of distant metastases spread. Abnormal levels of NK cell, CD8⁺ T cells, memory CD4⁺/CD4⁺, naïve CD4⁺/ CD4⁺, CD8⁺ HLA‐DR/CD8⁺, CD8⁺ CD38⁺/CD8⁺, and CD4⁺/CD8⁺ can be a potential blood biomarkers of cancer development. CD4+ T‐cell counts and percentages of CD8⁺ HLA‐DR/ CD8⁺ and CD8⁺ CD38⁺/ CD8⁺ can predict the cancer progression.

Immune checkpoint blockade (ICB) therapy has revolutionized cancer treatment, but its clinical benefit is limited in advanced gastric cancer (GC). Cancer-associated fibroblasts (CAFs) have been reported to be associated with ICB resistance, but the underlying mechanism has not been fully elucidated. Our previous single-cell RNA-seq analysis of GC revealed that POSTN+FAP+ extracellular matrix CAFs (eCAFs) communicate with macrophages. Here, we evaluated the correlation between eCAFs and ICB response in TCGA-STAD and real-world cohorts. Immune infiltration analysis and correlation analysis were performed to assess the relationship between eCAFs and macrophages. We first confirmed a negative correlation between the abundance of eCAFs and the overall response rate (ORR) to anti-PD-1 treatment in TCGA-STAD and real-world GC cohorts. Overexpression of POSTN in CAFs enhanced macrophage chemotaxis, while POSTN interference showed the opposite effect in vitro and in vivo. Furthermore, the cell density of POSTN+ CAFs was positively correlated with the infiltration level of CD163+ macrophages in GC patient tissues. The results demonstrated that POSTN secreted by CAFs enhances macrophage chemotaxis by activating the Akt signaling pathway in macrophages. Additionally, we found that POSTN+FAP+ eCAFs may exist in multiple solid tumors and are associated with ICB resistance. eCAFs promote macrophage chemotaxis through the secretion of POSTN, thereby leading to ICB resistance. High expression of POSTN is likely to predict a poor response to ICB. POSTN downregulation may be considered as a candidate therapeutic strategy to improve ICB efficacy.