Microbiota result from a symbiotic union between a host and certain microorganisms, helping to preserve the balance between human health and disease, as they directly influence the host’s metabolic, inflammatory and immune functions. The constant interaction between intestinal microbiota, the cells of the immune system, and the epithelium maintains intestinal homeostasis. This paper explains the scientific evidence supporting microbial influence in carcinogenesis, tumour progression, and the therapeutic efficacy of cancer drugs. Finally, it outlines the new challenges faced in therapeutics to enhance specific microbiota based on the therapeutic effectiveness needed.