Gastrointestinal cancers: Influence of gut microbiota, probiotics and prebiotics

• Gut microbiota is a key element for gastrointestinal cancers (especially of the colon and stomach)
• Carcinogenesis may be induced by gut microbiota through complex and various mechanisms
• Probiotics and prebiotics have anticarcinogenic effects, mainly in vitro and in animal studies
• In human GI cancers, probiotics and prebiotics are promising tools in prevention and/or therapy.

Cancers of the gastrointestinal (GI) tract continue to represent a major health problem, despite progress in therapy. Gut microbiota is a key element related to the genesis of GI cancers, countless papers addressing this burning issue across the world. We provide an updated knowledge of the involvement of gut microbiota in GI tumorigenesis, including its underlying mechanisms. We present also a comprehensive review of the evidence from animal and clinical studies using probiotics and/or prebiotics in the prevention and/or therapy of GI tumours, of GI cancer therapy-related toxicity and of post-operative complications. We summarize the anticarcinogenic mechanisms of these biotherapeutics from in vitro, animal and clinical interventions. More research is required to reveal the interactions of microflora with genetic, epigenetic and immunologic factors, diet and age, before any firm conclusion be drawn. Well-designed, randomized, double blind, placebo-controlled human studies using probiotics and/or prebiotics, with adequate follow-up are necessary in order to formulate directions for prevention and therapy.