Impact of EBRT ± concurrent chemotherapy on the multisite microbiota in locally advanced cervical cancer

Previous studies have confirmed that radiotherapy affects the vaginal and intestinal microbiota in cervical cancer patients, yet changes in microbiota across other body sites remain largely unexplored. This study aims to evaluate microbiome alterations across multiple body sites in patients with locally advanced cervical cancer (LACC) undergoing radiotherapy. Tumor tissue, vaginal fluid swabs, stool, urine, and oral swabs were collected from 33 patients with LACC receiving pelvic radiotherapy. Samples from baseline and on the day of the last fraction of external beam radiation therapy (EBRT) were analyzed. Microbiome analysis was conducted using 16 S v3–v4 ribosomal RNA (rRNA) gene sequencing. Comparisons of taxonomic composition, alpha diversity, and beta diversity were made between pre- and post-EBRT patients. Patients were divided into concurrent chemoradiotherapy (CCRT) and definitive radiotherapy alone (DRTA) cohorts. Post-EBRT, intra-tumoral alpha diversity decreased in both groups, while oral alpha diversity increased within the CCRT cohort. Significant alterations in beta diversity were observed across all five sites in both cohorts. Taxonomic profiling revealed marked intra-tumoral microbial remodeling toward aerobic taxa, accompanied by a decrease in dominant obligate anaerobes; similar reductions in obligate anaerobes were identified in vaginal, gut, and urinary microbiota. Vaginal microbiota consistently favored facultative anaerobes. Despite a reduction in gut obligate anaerobes, these taxa remained predominant. Urine samples were primarily colonized by facultative and obligate aerobes, while facultative and obligate anaerobes dominated the oral cavity. This study characterizes, for the first time, the global microbial profile across multiple body sites in LACC patients during EBRT. Although further research is warranted to elucidate underlying mechanisms, findings may provide novel insights for future investigations into microbiota as predictive biomarkers for LACC and for mitigating radiotherapy-associated complications.