Analysis of the fecal metagenome in pelvic radiation survivors with or without chronic gastrointestinal toxicity.

• DOI: 10.1200/jco.2024.42.16_suppl.e24041
• Publication Date: 2024-06-04T15:22:42Z
• Authors: Bailey Nelson; Senu Apewokin; Hope Esslinger; Jordan Kharofa

e24041 Background: Whole pelvis radiation therapy (WPRT) is often used as a definitive or adjuvant treatment in patients with genitourinary, gynecologic, and gastrointestinal (GI) malignancies. Irradiation of nearby bowel can cause acute and chronic GI symptoms, which can affect patients’ quality of life. Radiation therapy has been shown to alter the microbial flora and may select for pathogenic species, which may enhance toxicity. Characteristics of the fecal metagenome in patients with or without chronic GI toxicity is unknown. Severity of GI symptoms can vary between patients who receive a similar radiation dose to normal bowel; therefore, there is a critical need to evaluate the interaction of RT and microbial species in the development of toxicity. Methods: An institutional database was used to identify survivors that completed WPRT for prostate, gynecologic, and anal cancer within the last 5 years. Patients were excluded if they had evidence of recurrent disease requiring additional therapy. Eligible patients were asked to participate via telephone. Consenting patients provided a stool sample and completed a customized PRO-CTCAE form (scale 1-5) assessing chronic GI symptoms. Comprehensive shotgun metagenomics were performed on stool. Stool was sequenced using an Illumina NextSeq500. The fecal metagenome in patients with or without chronic GI symptoms were compared. Patients were dichotomized by PRO-CTCAE diarrhea score (0-1 [mild] vs ≥2 [moderate-severe]). Raw reads were processed with Kneaddata for trimming, Kracken2 for taxonomic profiling, and Bracken for abundance estimation for bacterial, fungal and viral genomes using sequences from the National Center for Bioinformatics to determine quantitative genus and species differences. For microbial diversity assessments, estimated inverse Simpson and Shannon indices were performed. Results: Fecal metagenome and PRO-CTCAE results were available for 13 survivors. Thirty percent (n = 4) of patients reported moderate to severe diarrhea. The mean age was 66 years, 38% were male, 46% received concurrent or adjuvant chemotherapy, and the mean time from completion of WPRT to stool analysis was 34 months (range 14-62 months). Conventional radiation bowel constraints were met for each patient. Several species were enriched in patients with mild GI toxicity. Notably, Akkermansia muciniphilia had the largest differential enrichment in patients with without chronic GI toxicity. Conclusions: In this cohort of patients, A. muciniphilia, a mucin-degrading bacteria that modulates the gut barrier integrity and mucin layer thickness, was enriched in patients with no to mild diarrhea compared to patients with moderate to severe diarrhea. A. muciniphilia supplementation has been shown to decrease systemic inflammation in Western diet-fed mice. Evaluation of A. muciniphilia as a radioprotective gut bacterium warrants further evaluation.