In the gastrointestinal tract, commensal microorganisms protect and maintain host homeostasis. From the expansion of the oncobiome, dysbiosis has been related to inflammation precipitating tumorigenesis and mediating the anticancer immune response. Thus, given the modulation of the intestinal ecosystem, biotherapeutics emerges as an adjuvant in cancer treatment. Thus, the present work aims to investigate the influence of the intestinal microbiota on neoplastic progression and therapeutic response. For this, a Narrative Literature Review was carried out on the PubMed platform, with the descriptors “Gastrointestinal Microbiome”, “Neoplasms” and “Biological Treatment”, associated with the Boolean operator “AND”, being structured in a final sample of 18 articles. The results suggest that ecological imbalance and changes in microbial metabolites, such as short-chain fatty acids (SCFAs), influence tumor progression and metastasis. Regarding the clinical response to chemotherapy/immunotherapy, it was demonstrated that Escherichia coli is one of the main species related to the increase in the metabolism of chemotherapy drugs, such as gemcitabine, decreasing its therapeutic efficacy. In contrast, the enrichment of certain strains leads to anticancer effects, such as Lactobacillus and Bifidobacterium. This modulation can occur by transplantation of fecal microbiota or by probiotic therapy with live or dead organisms or their metabolites, which act at different points of regulation. Thus, it is proposed that, despite the deleterious examples referring to tumor progression, the intestinal microbiota can also positively impact anticancer therapy. The auxiliary use of its elements constitutes a therapeutic promise in design.