# Association analysis of the differences in intestinal flora and clinical tumor indicators among colorectal cancer patients

## TL;DR

This study explores how gut bacteria differ in colorectal cancer patients compared to healthy individuals and how these differences relate to cancer progression.

## Contribution

The study systematically compares microbial diversity and function in cancerous, paracancerous, and fecal samples from CRC patients and healthy individuals.

## Key findings

- CRC patients show reduced microbial diversity and enrichment of pathogenic bacteria in cancerous tissues.
- Fecal samples from CRC patients have higher gut health index than cancerous tissues.
- Escherichia coli and Methylobacterium/Methylorubrum correlate with tumor size and stage.

## Abstract

Colorectal cancer (CRC) is the third most common malignant tumor globally, and its development is closely related to intestinal flora dysbiosis. However, the heterogeneity of cancerous tissues, paracancerous tissues, and fecal flora, and their clinical significance, has not been fully elucidated.

This study aimed to systematically analyze the diversity, composition, and functional differences of intestinal flora in patients with CRC compared to healthy individuals, and to reveal potential associations between the characteristics of these microbial communities and tumorigenesis and development.

Thirty CRC patients (30 cancerous tissue samples, 30 paracancerous tissue samples, and 30 fecal samples) and 30 healthy volunteers (30 fecal samples) were enrolled in the study. The microbial communities were analyzed using 16S rRNA sequencing, and the status of the bacterial flora was evaluated by combining alpha and beta diversity, species difference analysis, the Gut Microbiome Health Index (GMHI), and the Gut Microbiome Dysbiosis Index (MDI). The correlation of these factors with clinical parameters was then analyzed.

The alpha diversity of the cancerous tissue from patients with CRC was significantly lower than that of the fecal samples (p < 0.05). The intestinal microbiota of patients with CRC was statistically different from that of healthy individuals (p < 0.01). Additionally, there was a statistically significant difference in beta diversity between the cancerous tissue and fecal gut microbiota of patients with CRC (p < 0.01). The microbiota of the paracancerous tissues exhibited significantly higher GMHIs than the cancerous tissues. Healthy individuals demonstrated better gut health than individuals with CRC. The fecal samples from CRC patients had a higher GMHI than the cancerous tissues. The difference was statistically significant (p < 0.001). For MDI, however, the trend was reversed. A statistically significant positive correlation was observed between Escherichia coli and tumor size (p < 0.05). Similarly, Methylobacterium/Methylorubrum exhibited a statistically significant positive correlation with tumor stage (p < 0.05).The research found that Blautia and Faecalibacterium had higher abundances in the feces of healthy individuals and the tissues adjacent to colorectal cancer, while Escherichia-Shigella, Bacteroides, Enterococcus, and Fusobacterium had higher abundances in colorectal cancer tissues.

The intestinal flora of CRC patients is characterized by decreased diversity, an enrichment of pathogenic bacteria, and a reduction in protective flora. these microbial alterations are associated with tumor progression, potentially via inflammatory and metabolic pathways, although causal mechanisms remain to be functionally validated. The flora health index and dysbiosis index have potential for use as adjunctive diagnostic tools. However, individualized preventive intervention strategies need to be developed in the future by combining multi-omics data.