Cancer and the gut microbiome: the oncogenic impact of dysbiosis

Abstract Gut dysbiosis, defined as an imbalance in the gut microbiota’s composition and function, plays a key role in the development of cancer. It alters microbial diversity, disrupts immune function, weakens the gut barrier, and promotes long-term inflammation, contributing to tumour onset and progression. Contributing factors include diet, stress, disrupted sleep, inactivity, antibiotics, environmental exposures, and changes in host genetics or epigenetics. These factors reduce the production of protective microbial byproducts like short-chain fatty acids (SCFAs) and increase the formation of harmful compounds such as nitrosamines and secondary bile acids. Certain bacteria like Fusobacterium nucleatum , Helicobacter pylori , Escherichia coli (pks+), Bacteroides fragilis , and Streptococcus gallolyticus have been linked to cancer through their ability to cause inflammation, damage DNA, or interfere with immune detection. Based on this understanding, approaches such as probiotics, prebiotics, changes in diet, faecal microbiota transplantation (FMT), and targeted microbial treatments are being explored to restore microbial balance and reduce cancer risk. These findings highlight the microbiome’s role in the carcinogenetic pathway.