Abstract
Radiotherapy is a cornerstone treatment for pelvic and gastrointestinal malignancies, but radiation-induced gastrointestinal (GI) toxicity, including diarrhea, enteritis, and mucositis, remains a major clinical challenge. Emerging evidence implicates gut microbiome dysbiosis in the development and severity of these adverse effects.This systematic review synthesized findings from four studies evaluating associations between gut microbiota alterations and radiotherapy-induced GI toxicity across prostate, cervical, and rectal cancers.Radiotherapy was consistently associated with reduced microbial alpha diversity and altered beta diversity. Differential abundance of specific taxa, including Clostridium IV, Roseburia, Phascolarctobacterium, Coprococcus, and members of the Firmicutes and Bacteroidetes phyla, was observed in patients with GI toxicity. Pre-treatment dysbiosis, characterized by reduced diversity and altered Firmicutes/Bacteroidetes ratios, was associated with subsequent diarrhea and radiation enteropathy. Dysbiosis was also linked to systemic inflammatory responses and patient-reported fatigue, suggesting interactions among microbiome disruption, impaired mucosal barrier integrity, and systemic symptoms. Population-level differences in microbial composition further suggested potential effects of host-related factors. Gut microbiome dysbiosis may contribute to radiotherapy-induced GI toxicity and serve as a potential predictive biomarker for identifying high-risk patients. Future studies should employ larger cohorts, standardized microbiome assessment, and longitudinal designs to validate these associations and clarify causality.