P401 - Aerobic bacterial group as an early-stage biomarker from faecal samples of patients with colorectal cancer without distant metastasis

Purpose/Background: Colorectal cancer (CRC) is one of the leading causes of cancer-related deaths worldwide, with early detection significantly improving patient survival rates. However, current screening methods, such as fecal occult blood tests (FOBT) and colonoscopies, lack the sensitivity and specificity needed to detect early-stage CRC. Recent research has suggested that changes in the gut microbiome may provide biomarkers for CRC detection. This study aims to identify aerobic bacterial groups as early-stage, non-invasive biomarkers for patients with CRC without distant metastasis, focusing on patients without key genetic mutations (KRAS, NRAS, BRAF) or microsatellite instability.

Methods/Interventions: A total of 92 stool samples from CRC patients were analyzed using 16S rRNA gene sequencing and compared to 745 healthy control samples. Patients were grouped according to the TNM classification, with distinctions made between those with only tumor involvement (T group) and those with lymph node metastasis (TN group). The gut microbiota was characterized using metagenomic sequencing, and specific aerobic bacterial species were identified in patients without lymph node metastasis. CatBoost, a machine learning algorithm, was employed to assess the diagnostic accuracy of these microbial markers, which was validated using quantitative PCR (qPCR).

Results/Outcomes: Significant differences were observed in the gut microbiota between CRC patients and healthy individuals. Seven aerobic bacterial genera (Rhodococcus, Stenotrophomonas, Delftia, Psychrobacter, Devosia, Sphingobacterium, and Ensifer) were found to be highly prevalent in early-stage CRC patients without lymph node metastasis but were absent in those with lymph node involvement. The diagnostic prediction model achieved an area under the curve (AUC) of 0.8, indicating high diagnostic accuracy. Functional analyses also revealed differences in metabolic pathways between the T and TN groups, particularly in xenobiotic and terpenoid metabolism.

Conclusion/Discussion: This study identifies a distinct set of aerobic bacterial genera as potential biomarkers for the early detection of CRC in patients without distant metastasis. The findings suggest that these microbes may play a significant role in the gut environment before lymph node metastasis occurs, offering a non-invasive method for early CRC diagnosis. Further research is needed to validate these findings and investigate the underlying mechanisms by which these microbial communities contribute to CRC progression. If validated, these biomarkers could enhance the effectiveness of CRC screening programs and improve patient outcomes.

Fig 1.
This figure shows a comparison of the overall and gender-specific microbiota analysis between the T (non-lymph node metastasis) and TN (lymph node metastasis) groups within different cancer stages. It includes linear discriminant analysis (LDA) results highlighting key bacterial genera that differ between these groups, which is crucial to understanding the study’s discovery of early-stage biomarkers for colorectal cancer without lymph node metastasis. It demonstrates how specific aerobic bacteria, which are potential markers, are present in the T group but absent in the TN group, divided by gender.

Fig 2.
This figure focuses on the prediction of early colorectal cancer-specific fecal microbiome markers using the CatBoost algorithm. It includes results showing the relative abundance of the top 20 and seven targeted bacterial genera in 92 CRC samples. The ROC curve and AUC value demonstrate the high accuracy of the model in distinguishing between T and TN groups, making it a key figure supporting the study's conclusions about the diagnostic potential of specific microbiota.