Abstract 758: Comparative Microbiome Analysis of Paired Mucosal and Fecal Samples in Korean Colorectal Cancer Patients
Authors: Lee Sanghun 
Published: March 2024

Abstract
Background Beyond the known risk factors such as age over 50, unhealthy diet, ethnicity, and smoking, emerging evidence suggests that gut microbial dysbiosis plays a crucial role in the early stages of colorectal cancer (CRC) by contributing to chronic inflammation and various intestinal dysfunctions. Even though various bacterial species have been studied, the gut microbiome profile as a representative biomarker in CRC patients remains largely unreported. This study presents a comparative analysis of the microbiome profiles of fecal and mucosal samples from CRC patients, followed by metagenomic profiling investigation to validate dominant bacteria in each sample type of CRC patients.
Methods The study involved 12 patients receiving CRC resection at Myongji Hospital in South Korea, recruited from May 2020 to June 2021. Fecal samples were collected pre-surgery, and mucosal samples during surgery. Paired-end sequencing was performed using Illumina MiSeq (Illumina, San Diego, USA) platform. 16s rRNA gene-based microbiome profiling was analyzed using QIIME2 (V.2020.11), a plugin-based platform for microbiome analysis. Sequencing reads were filtered, denoised, and clustered into amplicon sequence variants (ASVs) using DADA2 included in QIIME2. Taxonomic classification was assigned in the QIIME2 pipeline using a pre-trained classifier based on the Silva 138.1 reference sequence. Linear discriminant analysis (LDA) effect size (LEfSe) analysis was performed with LDA score ≥3.0 and p-value of 0.05.
Results The study subjects included 12 Korean patients, with an average age of 71 ± 10 years. The gender distribution included 3 men and 9 women whose body mass index was 24.6 ± 2.4 (mean ± SD). There was significant difference observed in UniFrac beta-diversity between the two groups (p=0.001). The relative taxonomic patterns of the microbiota between CRC stool and tissue showed that Bacteroides and Fusobacterium were more dominant in tissue than stool at both phylum and genus levels. Further taxonomic differences between the samples revealed that Firmicutes, Bacilli, and Lactobacillacease were over-represented in CRC patient stool, while Pseudomonadales (p&lt;0.001) and Pseudomonas (p&lt;0.001) were identified in the mucosal tissue.
Conclusion Our findings revealed that notable distinction was observed in the beta-diversity, indicating a unique microbial composition in tissue. Specifically, higher prevalence of Bacteroides and Fusobacterium at the genus level were identified in tissue. Additionally, our analysis highlighted Pseudomonadales and Pseudomonas emerged in CRC mucosal tissues. Furthermore, by comparing with a healthy control group, we aim to further elucidate potential markers unique to CRC patients.
Citation Format: Sanghun Lee. Comparative Microbiome Analysis of Paired Mucosal and Fecal Samples in Korean Colorectal Cancer Patients [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(6_Suppl):Abstract nr 758.