18 October 2011

Oral bacteria linked to colon cancer

by Kate Melville

The discovery of a strikingly large number of Fusobacterium cells in colorectal tumor samples has prompted researchers to consider that the bacteria primarily found in dental plaque may play a role in causing colon cancer. The researchers, from the Dana-Farber Cancer Institute and the Broad Institute, have published their findings in the journal Genome Research. Details of corroborative research from the BC Cancer Agency and Simon Fraser University in Canada appear in the same edition of the journal.

A confirmed connection between periodontal Fusobacterium and colorectal cancer would mark the first time any microorganism has been found to play a role in this type of cancer, which is the second leading cause of cancer deaths in the US.

The discovery was made by sequencing the DNA within samples of normal colon tissue and nine of colorectal cancer tissue, and validated by sequencing paired DNA samples from normal colon tissue and colon cancer tissue.

"Tumors and their surroundings contain complex mixtures of cancer cells, normal cells, and a variety of microorganisms such as bacteria and viruses," explains the study's senior author, Matthew Meyerson, of Dana-Farber. "Over the past decade, there has been an increasing focus on the relationship between cancer cells and their 'microenvironment,' specifically on the cell-to-cell interactions that may promote cancer formation and growth."

In some respects the new findings echo previous Australian research that established the causative relationship between the bacterium Helicobacter pylori and stomach cancer.

The new study notes that while the relationship between colorectal cancer and Fusobacterium remains unclear, there are intriguing hints that the bacterium may play a role in the cancer. Previous studies have suggested that Fusobacterium is associated with inflammatory bowel diseases such as ulcerative colitis.

"At this point, we don't know what the connection between Fusobacterium and colon cancer might be," Meyerson cautions. "It may be that the bacterium is essential for cancer growth, or that cancer simply provides a hospitable environment for the bacterium. Further research is needed to see what the link is."

Comparison studies of Fusobacterium levels in a larger number of patients with colorectal cancer are planned as are studies to determine whether the bacterium can be used to induce colon cancer in animal models.

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Source: Dana-Farber Cancer Institute