The mucosal microbiome of right-sided CRC was distinctly different from the mucosal microbiome of left-sided CRC patients, suggesting distinct microbial ecology and heterogeneous host-microbial ecologic relationships that may contribute to differences in the tumor microenvironment between left- and right-sided CRC.
CRC was associated with alterations in both fecal and mucosal microbiomes compared to healthy controls.
The overall composition of the mucosal microbiome, stratified by metacommunities, differed between patients with left- and right-sided neoplastic lesions.
Patients with right-sided CRC had an elevated inter-phylum ecologic network compared to left-sided CRC.
Patients with left-sided CRC had an enriched abundance of Fusobacterium compared to right-sided CRC.
Rectal neoplasia harbored a tumor microbiome that was distinctly different from the tumor microbiome at other anatomic sites.
Multiple sample types—stool, colonic aspirate, and mucosal biopsy—were collected to comprehensively profile the intestinal microbiome across compartments.
This research suggests that the community of microbes living in and around colorectal tumors is not uniform—it varies significantly depending on where in the colon or rectum a tumor is located. The researchers collected nearly 700 samples (stool, gut fluid, and tissue biopsies) from healthy individuals, patients with precancerous polyps (adenomas), and patients with colorectal cancer (CRC). They found that colorectal cancer overall is associated with changes in the gut microbiome, but more importantly, the microbial patterns in tumors on the right side of the colon were distinctly different from those on the left side. Right-sided tumors showed more complex interactions between different groups of bacteria (elevated inter-phylum ecological networks), while left-sided tumors had higher levels of a specific bacterium called Fusobacterium, which has previously been linked to colorectal cancer. Rectal tumors were found to have their own unique microbial profile, different from tumors elsewhere in the colon. These findings matter because left- and right-sided colorectal cancers are already known to behave differently clinically—they respond differently to treatments and have different survival outcomes. This research suggests that the microbial environment of the tumor may be one reason for these differences. Understanding how bacteria differ between tumor locations could help explain why these cancers behave differently and might eventually point toward location-specific diagnostic markers or treatments. The study also highlights that using multiple types of samples (stool, tissue, gut fluid) gives a more complete picture of these microbial communities than any single sample type alone.
Wong S, Kwong T, Zhang R, Lam T, Ho A, Leung W, et al.. (2026). Comprehensive microbiome profiling reveals mucosal microbiome heterogeneity in patients with left- and right-sided colorectal neoplasia.. Cancer biology & medicine. https://doi.org/10.20892/j.issn.2095-3941.2025.0846