Effects of gut microbiome and obesity on the development, progression and prevention of cancer (Review)

Cancer is one of the leading causes of death worldwide and it is estimated that the mortality rate of cancer will increase in the coming years. The etiology of the development and progression of cancer is multifactorial. Insights have been gained on the association between the human microbiome and tumor cell malignancy. A number of commensal microbe species are present in the human gut. They serve pivotal roles in maintaining several health and disease conditions, such as inflammatory bowel disease, irritable bowel syndrome, obesity and diabetes. Known major factors involved in cancer development include age, hormone levels, alcohol consumption, diet, being overweight, obesity, and infections, regardless of the type of cancer. Therefore, the present review aims to discuss the relationship between the gut microbiome and obesity-associated malignancies, including colorectal, gastric and liver cancer. Obesity has been reported to contribute to the development of numerous types of cancer primarily caused by high fatty food intake. In addition, obesity-associated microbiome alterations can lead to cancer and its progression. Dysbiosis of the gut microbiota can alter the metabolite profile, whilst increasing the levels of toxins, such as Bacteroides fragilis toxin and colibactin and cytolethal distending toxin, which are responsible for oncogenesis. The present review provides insights into the impact of gut microbiome dysbiosis on the progression of different types of cancers associated with obesity. It also discusses possible strategies for preserving a healthy gut microbiome. Different pre-clinical and clinical models are available for studying cancer development downstream of gut microbiome dysbiosis. Furthermore, the role of metabolites or drugs employed in colorectal, gastric and liver cancer therapy would be discussed.