Association between gut microbial change and acute gastrointestinal toxicity in patients with prostate cancer receiving definitive radiation therapy

Background This prospective study investigated the association between gut microbial changes and acute gastrointestinal toxicities in prostate cancer patients receiving definitive radiation therapy (RT). Methods Seventy‐nine fecal samples were analyzed. Stool samples were collected at the following timepoints: pre‐RT (prRT), 2 weeks after the start of RT (RT‐2w), 5 weeks after the start of RT (RT‐5w), 1 month after completion of RT (poRT‐1 m), and 3 months after completion of RT (poRT‐3 m). We computed the microbial community polarization index (MCPI) as an indicator of RT‐induced dysbiosis. Results Patients experiencing toxicity had lower alpha diversity, especially at RT‐2w (p = 0.037) and RT‐5w (p = 0.003). Compared to patients without toxicity, the MCPI in those experiencing toxicities was significantly elevated (p = 0.019). In terms of predicted metabolic pathways, we found linearly decreasing pathways, including carbon fixation pathways in prokaryotes (p = 0.035) and the bacterial secretion system (p = 0.005), in patients who experienced toxicities. Conclusions We showed RT‐induced dysbiosis among patients who experienced toxicities. Reduced diversity and elevated RT‐related MCPI could be helpfully used for developing individualized RT approaches.