Bacterium Linked to Colorectal Cancer

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Bacterium Linked to Colorectal Cancer in Two Independent Studies

Two independent research groups have identified a bacterium that is associated with colorectal cancer in the first studies to identify a potential link between this common cancer and an infectious agent. Further research is needed, however, to validate the findings and determine whether the bacterium plays a causative role in colorectal cancer, researchers from both groups stressed. The studies were published online October 18 in Genome Research.
The microbe Fusobacterium is not abundant in the human colon, which houses trillions of bacteria and thousands of microbial species. Nevertheless, Fusobacterium species have been associated with a number of conditions, including inflammatory bowel diseases, such as ulcerative colitis, an established risk factor for colorectal cancer.
The two research groups used similar approaches in their studies. A British Columbia Cancer Agency team, led by Dr. Robert Holt, initially identified an overabundance of Fusobacterium by analyzing 11 colorectal tumor samples and adjacent healthy colon tissue from the same patients using high-throughput RNA sequencing. A group from the Broad Institute at the Massachusetts Institute of Technology and Harvard University, led by Dr. Matthew Meyerson, used whole-genome sequencing to identify bacterial DNA in 9 paired cancerous and normal colon tissue samples.
Both groups used polymerase chain reaction (PCR) technology to validate the findings in a larger group of paired cancerous and normal colon tissue samples (88 and 95 samples, respectively).
Among the samples analyzed by Dr. Holt and his colleagues using PCR, “the mean overall abundance of Fusobacterium was found to be 415 times greater in the tumor samples…than in the matched normal samples,” they reported. Although Dr. Meyerson’s group had similar findings, “only a subset of the cancers showed dramatic enrichment of Fusobacterium species,” they noted.
Dr. Meyerson and his colleagues also found Fusobacterium in 2 out of 11 samples of colorectal cancer metastases.
“The presence of this bacterium may simply represent an opportunistic infection at an immunocompromised site, but the possibility of a role in tumor etiology, perhaps through pro-inflammatory mechanisms, deserves further scrutiny,” Dr. Holt and his colleagues wrote.
The bacterial composition of the tumors analyzed and their matched control tissue were more similar to each other than the bacterial composition of tumor samples from different patients, noted Phil Daschner of NCI’s Division of Cancer Biology. This suggests that “a patient’s gastrointestinal ecosystem—including the individual’s genetics, other bacteria, and cellular- and dietary-derived components and metabolites—is more important in shaping the microbial communities in the tumor than the tumor's microenvironment,” he continued.
The findings also suggest the possibility that prevention, diagnosis, and treatment strategies could be formulated based on the colon’s bacterial makeup, Daschner noted