The Microbiome and Cancer: Creating Friendly Neighborhoods and Removing the Foes Within

Abstract

The human body is colonized by the microbial cells that are estimated to be as abundant as human cells, yet their genome is roughly 100 times the human genome, providing significantly more genetic diversity. The past decade has observed an explosion of interest in examining the existence of microbiota in the human body and understanding its role in various diseases including inflammatory bowel disease, neurologic diseases, cardiovascular disorders, and cancer. Many studies have demonstrated differential community composition between normal tissue and cancerous tissue, paving the way for investigations focused on deciphering the cause-and-effect relationships between specific microbes and initiation and progression of various cancers. Also, evolving are the strategies to alter tumor-associated dysbiosis and move it toward eubiosis with holistic approaches to change the entire neighborhood or to neutralize pathogenic strains. In this review, we discuss important pathogenic bacteria and the underlying mechanisms by which they affect cancer progression. We summarize key microbiota alterations observed in multiple tumor niches, their association with clinical stages, and their potential use in cancer diagnosis and management. Finally, we discuss microbiota-based therapeutic approaches.

Insulin Resistance and Cancer: In Search for a Causal Link

“…It is well recognized that microbiota can impact on gut and systemic host metabolism through several mechanisms such as the maintenance of gut barrier integrity, the ability to absorb energy from digested nutrients, the production of metabolites (i.e., short chain fatty acids (SCFAs), secondary bile acids, endotoxins) and gut-derived hormones (i.e., GLP-1, GIP, PPY) that affect satiety and/or peripheral insulin sensitivity, and the modulation of epigenetic modifications [ 278 ]. Therefore, it may come as no surprise that gut dysbiosis could be linked to various human diseases, including cancer, by influencing the genomic stability of host cells through the modulation of many different signaling pathways [ 279 ]. Previous studies have reported a correlation between low gut microbiota richness (i.e., low bacterial gene count) and metabolic dysfunction, including IR, dyslipidemia, excess adiposity, and inflammation [ 275 ].…”

The Multifaceted Roles of Diet, Microbes, and Metabolites in Cancer

“…More recent research has highlighted the role of the local microbiome of the tumour microenvironments outside of the gut; for example, a Mediterranean diet has been shown to alter the microbiome of the breast by increasing the abundance of microbes, such as Lactobacillus, when compared to a western diet [79]. Further, studies have begun to identify a series of distinct tumour-specific microbiomes associated with select cancers [80][81][82], which can be associated with therapeutic response [83,84]. Understanding these distinct microbe profiles may allow for early detection in the future, or allow for preventative measures through microbe-altering therapies or dietary interventions.…”

Gut Microbiome and Cellular Senescence in the Context of Aging and Disease: An Emerging Frontier

“…Numerous studies have shown altered gut microbioata composition during the development of various cancers including but not limited to colorectal cancer (Nakatsu et al, 2015), gastric cancer (Ferreira et al, 2018), lung cancer (Zhuang et al, 2019), pancreatic cancer (Half et al, 2019), prostate cancer (Daisley et al, 2020), breast cancer (Goedert et al, 2015), brain cancer (D'Alessandro et al, 2020) and even leukemia (Vicente-Dueñas et al, 2020). Mechanistically, the gut microbiome can influence tumorigenesis at sites distant to the gut by regulating circulatory levels of metabolites and nutrients as well as through the release of microbial toxins which are currently under intense investigation (Parida and Sharma, 2021). Changes in the gut microbiota community has also been documented in the pathogenesis of age-related cardiovascular disorders such as heart failure and coronary artery diseases.…”