Background: Cancer is a lethal disease that results from a multifactorial process. Progression into carcinogenesis and an abnormal cell proliferation can occur due to the micro and macro environment as well as genetic mutations and modifications. In this review, cancer and the microbiota – mainly bacteria that inhabit the tumour tissue – have been discussed. The positive and negative impacts of the commensal bacteria on tumours being protective or carcinogenic agents, respectively, and their strategies have also been described. Methods: Related published articles written in English language were searched from Google Scholar, PubMed, Mendeley suggestions, as well as Google search using a combination of the keywords ‘Microbiota, commensal bacteria, cancer, tumor’. Relevant literature published between the years 1979 and 2018 were included in this review. Results: The complicated nature of cancer as well as the role that might be played by the commensal bacteria in affected tissues have been the focus of the recent studies. The symbiotic relationships between the microbiota and the host have been shown to confer benefits to the last. By contrast, the microbiota has been suggested to upgrade cancer by modifying the balance of host cell proliferation and death, by provoking chronic inflammation, and by eliciting uncontrolled innate and adaptive immunity. In this context, aerobic and anaerobic bacteria have been isolated from various tumor samples. Conclusions: It can be concluded that commensal microbiota plays an important role in the prevention of diseases including cancer. Inversely, microbiota alterations (dysbiosis) have been found to interrupt that symbiotic correlation between the host and the inhabitant microbiota probably leading to cancer. Recommendations: The correlation between the commensal microbiome, antibiotics uptake and cancer occurrence need to be investigated exclusively. Moreover, increased attention must be paid to evaluating the effects of these microorganisms on the currently used anticancer agents, and the role that might be played by commensal bacteria on tumor progression or tumor regression.
