Gut Microbiome Components Predict Response to Neoadjuvant Chemoradiotherapy in Patients with Locally Advanced Rectal Cancer: A Prospective, Longitudinal Study

The gut microbiome is involved in antitumor immunotherapy and chemotherapy responses; however, evidence-based research on the role of gut microbiome in predicting response to neoadjuvant chemoradiotherapy (nCRT) in patients with locally advanced rectal cancer (LARC) remains scarce. This prospective, longitudinal study aimed to evaluate the feasibility of the gut microbiome in predicting nCRT responses. We collected 167 fecal samples from 84 patients with LARC before and after nCRT and 31 specimens from healthy individuals for 16S rRNA sequencing. Patients were divided into responders and nonresponders according to pathologic response to nCRT. After identifying microbial biomarkers related to nCRT responses, we constructed a random forest classifier for nCRT response prediction of a training cohort of baseline samples from 37 patients and validated the classifier in another cohort of 47 patients. We observed significant microbiome alterations represented by a decrease in LARC-related pathogens and an increase in and during nCRT. Furthermore, a prominent microbiota difference between responders and nonresponders was noticed in the baseline samples. Microbes related with butyrate production, including , and , were overrepresented in responders, whereas and were overrepresented in nonresponders. Ten biomarkers were selected for the response-prediction classifier, including , and , which yielded an area under the curve value of 93.57% [95% confidence interval (CI), 85.76%-100%] in the training cohort and 73.53% (95% CI, 58.96%-88.11%) in the validation cohort. The gut microbiome offers novel potential biomarkers for predicting nCRT responses, which has important manifestations in the clinical management of these patients.