A signature that unifies the colorectal cancer microbiota across multiple studies has not been identified.
In addition to methodological variance, heterogeneity may be caused by both microbial and host response differences, which was addressed in this study.
Dr Flemer Burkhardt and colleagues prospectively studied the colonic microbiota, and the expression of specific host response genes using fecal and mucosal samples from 59 patients undergoing surgery for colorectal cancer, 21 individuals with polyps, and 56 healthy controls.
Microbiota composition was determined by 16S rRNA amplicon sequencing.
Expression of host genes involved in colorectal cancer progression and immune response was quantified by real-time quantitative PCR.
|Colorectal cancer-associated co-abundance groups were differentially correlated with the expression of host immunoinflammatory response genes|
The team found that the microbiota of patients with colorectal cancer differed from that of controls, but alterations were not restricted to the cancerous tissue.
The research team detected differences between distal and proximal cancers, and fecal microbiota only partially reflected mucosal microbiota in colorectal cancer.
Patients with colorectal cancer can be stratified based on higher level structures of mucosal-associated bacterial co-abundance groups that resemble the previously formulated concept of enterotypes.
Of these, Bacteroidetes Cluster 1 and Firmicutes Cluster 1 were in decreased abundance in colorectal cancer mucosa, whereas Bacteroidetes Cluster 2, Firmicutes Cluster 2, Pathogen Cluster and Prevotella Cluster showed increased abundance in colorectal cancer mucosa.
The team noted that colorectal cancer-associated co-abundance groups were differentially correlated with the expression of host immunoinflammatory response genes.
Dr Burkhardt's team concludes, "Colorectal cancer-associated microbiota profiles differ from those in healthy subjects and are linked with distinct mucosal gene-expression profiles."
"Compositional alterations in the microbiota are not restricted to cancerous tissue and differ between distal and proximal cancers."