Abstract 2805: Shotgun sequencing of serial fecal microbiome samples in patients with colorectal cancer reveals distinct bacterial species and metabolic pathways associated with tumor sidedness and age at diagnosis

Abstract Background: The incidence of early onset (EO) colorectal cancer (CRC) (age 50) is rising with a left-sided predominance. Response to chemotherapy and anti-EGFR therapies differ in left- and right-sided colon cancers after accounting for genomic differences. The intestinal microbiome may contribute to CRC pathogenesis and response to therapy; how organisms drive metastasis and treatment resistance is not known. Purpose: To define the microbiome contribution to EO-CRC and response to treatment by analyzing longitudinal samples from previously untreated patients with CRC. Methods: We designed a prospective biospecimen collection platform and selected patients with previously untreated CRC. We collected stool, biopsy or surgical tissue, and peripheral blood mononuclear cells at baseline and serially throughout treatment. Stool samples were analyzed using shotgun sequencing. Alpha diversity was calculated using the inverse Simpson index and compared between groups using the Wilcoxon signed-rank test. Beta diversity was analyzed using the Bray-Curtis dissimilarity matrix and compared using PERMANOVA. Multivariate associations between species abundance, metabolic pathway abundance and clinical covariates were performed using MaAsLin2 R package. Results: We analyzed a total of 132 stool samples from 65 patients with CRC including up to 5 samples from a single patient over time. Mean alpha diversity did not differ significantly by primary site, stage or age at diagnosis. Beta diversity was significantly different between samples from right- compared with left-sided CRC (P=. 011) and pre- and post-surgery (P=. 001). Beta diversity also differed significantly by diagnosis age (50 vs. 50) (P=. 001 all samples, P=. 032 baseline samples). When CRC baseline samples were examined at the species level, Blautia glucerasea was associated with right-sided primary (P. 001, Q=. 1). Considering non-metastatic cases, recurrence was associated with increased Enteroscipio rubneri, Actinomyces oral taxon 448, Bacteroidales sp. and Lancefieldella parvula (P. 01, Q0. 1). We further investigated metabolic pathway associations. The superpathway of L-threonine metabolism was significantly increased in samples from patients with right-sided colon cancer at baseline (P. 001, Q=. 03). Considering samples across all time points, right-sided colon cancer was associated with increased abundance of pathways associated with propanoate degradation, L-threonine metabolism, yeast NADPH production, and hydroxyphenylacetate degradation (all P. 001, Q. 05). Conclusions: The functional effects of the intestinal microbiome may underlie the distinct biology of right-sided colon cancer. Composition of the intestinal microbiome differs by age at diagnosis. Updated recurrence data will be presented. Citation Format: Melissa Lumish, Nicholas Waters, Joshua Leinwand, Asha Saxena, Anqi Dai, Teng Fei, Maggie Fox, Andre Chavez, Jonathan Bermeo, Dorina Ismailgeci, Elizabeth Benitez, Christopher Cowley, Julio Garcia-Aguilar, Martin Weiser, Andrea Cercek, Luis A. Diaz, Marcel van den Brink, Jonathan Peled, Karuna Ganesh. Shotgun sequencing of serial fecal microbiome samples in patients with colorectal cancer reveals distinct bacterial species and metabolic pathways associated with tumor sidedness and age at diagnosis abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2805.