Intratumor microbiome in cancer progression: current developments, challenges and future trends

Abstract

Cancer is a complicated disease attributed to multifactorial changes, which causes difficulties with treatment strategies. Various factors have been regarded as the main contributors, and infectious etiological factors have recently attracted interest. Several microbiomes contribute to carcinogenesis, cancer progression, and modulating cancer treatment by inducing cancerous epithelial cells and chronic inflammation. Most of our knowledge on the role of microbiota in tumor oncogenesis and clinical efficiency is associated with the intestinal microbiome. However, compelling evidence has also confirmed the contribution of the intratumor microbiome in cancer. Indeed, the findings of clinical tumor samples, animal models, and studies in vitro have revealed that many intratumor microbiomes promote tumorigenesis and immune evasion. In addition, the intratumor microbiome participates in regulating the immune response and even affects the outcomes of cancer treatment. This review summarizes the interplay between the intratumor microbiota and cancer, focusing on the contribution and mechanism of intratumor microbiota in cancer initiation, progression, and potential applications to cancer therapy.

Keywords: Anticancer treatment; Immune system; Intratumor microbiome.

Fig. 1

Intratumor microbiota niches across cancer types. Microbiota are detected in multiple solid tumors, including liver, bladder, kidney, prostate, pancreatic, brain, esophageal, colon, gastric, lung, breast, oral and gynecologic cancers. The intratumor microbiome has been convinced to contribute to the carcinogenesis, cancer progression and drug resistance

Fig. 2

Potential molecular mechanisms by which intratumor microbiota promote carcinogenesis. A. Microbiome contributed to the tumorigenesis through inducing DNA damage, Wnt/β-catenin pathway, EMT process, p53 degradation, chronic inflammation and protein translocation. B. The chronic inflammation that induced by intratumor microbiota include cancer-associated inflammation, cancer-associated cytokines and ROS/NS production, inhibited cytotoxic immune cells infiltration and function and enhanced immunosuppressive cells infiltration and polarization

Fig. 3

The potential source of intratumor microbiota. A. Microbiome may translocate from intestine to the tumor sites, which depends on blood circulation and ducts translocation. B. Oral microbiome may be another origin of intratumor microbiota. And blood circulation and digestive system are the main pathways

Fig. 4

The utilization of intratumor microbiota data in cancer screen and treatment. A. Data from clinical samples may facilitate the development of new cancer screen and prognosis, including microbiota patterns from tumor sites and easily accessible samples. B. Intratumor microbiota may be applied for cancer treatment, including engineering bacteria, diet modulation, fecal microbiome transplantation, antibiotics and intratumor microbiome injection