Differences in the On- and Off-Tumor Microbiota between Right- and Left-Sided Colorectal Cancer.

Area of Science:

• Microbiology
• Gastroenterology
• Oncology

Background:

• The gut microbiota plays a crucial role in colorectal cancer (CRC) development and progression.
• Distinct microbial communities exist in the right and left colon, but their role in CRC is not fully understood.

Purpose of the Study:

• To investigate differences in the on- and off-tumor microbiota between patients with right-sided and left-sided colorectal cancer.
• To compare the taxonomic composition and diversity of the gut microbiome at different locations within the colon in CRC patients.

Main Methods:

• 16S ribosomal RNA sequencing was used for microbiome profiling.
• Tumor and adjacent biopsies were collected from patients with right-sided (n=17) and left-sided (n=7) colorectal adenocarcinoma.
• Alpha and beta diversity analyses were performed to assess microbial community structure.

Main Results:

• Off-tumor microbiota diversity differed significantly between right- and left-sided CRC patients.
• Right colon off-tumor samples were enriched with Lachnoclostridium, Selenomonas, and Ruminococcus genera.
• Left colon off-tumor samples were enriched with Epsilonbacteraeota, Campylobacteria, Pasteurellales, and Campylobacterales.
• On-tumor microbiota showed fewer differences between tumor locations, with left tumors enriched in Methylophilaceae, Vadin BE97, Alloprevotella, Intestinibacter, Romboutsia, and Ruminococcus 2.
• Left-sided CRC patients exhibited greater taxonomic differences between paired on- and off-tumor microbiota compared to right-sided CRC patients.

Conclusions:

• The right and left colon harbor distinct bacterial populations.
• Colorectal tumors induce a more consistent microbiota composition between tumor locations, overriding some site-specific differences.
• These findings highlight the impact of CRC on the gut microbiome and suggest location-specific microbial alterations.