Effect of chemotherapy on gut microbiota in patients with colorectal cancer

The gut microbiota plays a crucial role in digestion, energy conversion, immune regulation, and disease resistance. Research has established a link between gut microbiota and the development and progression of colorectal cancer (CRC), noting variations in their composition within and around tumors, and gut microbiota may impact the effectiveness of drug therapies. Chemotherapy remains the cornerstone of CRC treatment, yet studies exploring its relationship with gut microbiota are still limited. In this study, we selected 20 patients with colorectal adenocarcinoma to investigate changes in their gut microbiota before and after chemotherapy using 16S rRNA sequencing. All participants received the FOLFOX6 chemotherapy regimen, and fecal samples were collected pre- and post-treatment, aiming to elucidate the connection between chemotherapy and gut microbiota by analyzing alterations in microbial composition, diversity, and richness across different chemotherapy cycles. Following the first chemotherapy cycle, we observed a decline in gut microbiota richness among CRC patients, along with notable shifts in microbial composition. Specifically, the phyla Firmicutes and Bacteroides decreased, while Proteobacteria, Actinobacteria, and Verrucomicrobia increased in abundance. As chemotherapy cycles progressed, microbial composition stabilized, with no further significant changes noted. KEGG functional gene prediction analysis indicated that chemotherapy-induced alterations in gut microbiota composition were linked to common chemotherapy side effects, including metabolic, immune, hematological, and neurological disturbances. In conclusion, our findings suggest that chemotherapeutic agents influence the gut microbiota composition in CRC patients, and these microbial changes may be associated with chemotherapy-related adverse effects.