Two new studies, one of them involving researchers from B.C., are drawing the first intriguing link between colorectal cancer and a specific kind of bacteria.
The studies found Fusobacterium bacteria are many times more prevalent in colorectal tumours than in normal tissue.
But what remains a mystery is whether the bacteria are the result of the cancer or whether they helped cause it.
The studies were conducted separately -- one in B.C. and one in Boston -- but both have been published at the same time in the journal Genome Research.
The authors of both papers note that many cancers have already been linked to infectious viruses and bacteria. For example human papillomavirus, or HPV, is considered the primary cause of cervical cancer, Helicobacter pylori bacteria can cause stomach cancer, and some strains of hepatitis can lead to liver cancer.
Rob Holt, an associate professor of molecular biology and biochemistry at Simon Fraser University, a B.C. Cancer Agency scientist and a senior author of one of the reports, says since bacteria are linked to other digestive cancers, his team wanted to know whether colorectal cancers might be linked too.
They analyzed genetic material in samples of colorectal tumors from 11 patients and compared them to samples of normal colon tissue. After eliminating all the human genes from their analysis, they spotted huge numbers of Fusobacterium genes.
Their discovery was a surprise, Holt says; Fusobacterium is not normally among the more prominent bacteria species in the gut.
Meanwhile in Boston, Dr. Matthew Meyerson and his colleagues at the Dana-Farber Cancer Institute in Boston were conducting similar research.
They analyzed genetic material from the tumours of nine colorectal cancer patients, and compared them to nine samples of healthy colon tissue. They also found unusually large amounts of Fusobacterium's genetic signature.
Their paper was also published Tuesday in Genome Research.
If the link between colon cancer and Fusobacterium can be confirmed, it would mark the first time any microorganism has been found to play a role in colon cancer, which is one of the leading causes of cancer deaths in Canada.
Previous studies have suggested that Fusobacterium is associated with inflammatory bowel diseases, such as ulcerative colitis. Those diseases are already known to raise people's risk of developing colon cancer.
"At this point, we don't know what the connection between Fusobacterium and colon cancer might be," Meyerson said in a separate statement.
"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."
Holt says that if Fusobacterium is proven to be a cause of colorectal cancer, then targeting the bacteria with antibiotics or vaccines could provide a new way to prevent and treat the disease.
Researchers are now working on comparison studies of Fusobacterium levels in bigger groups of patients, again comparing those with colorectal cancer and those without the disease.
Studies are also in the planning stages that would determine whether introducing Fusobacterium in lab animals would induce colon cancer.
Meyerson's study was supported by grants from the U.S. National Cancer Institute, the National Human Genome Research Institute, and the Starr Cancer Consortium.
Holt's study was funded by Genome BC, the Canadian Institutes of Health Research (CIHR), and the BC Clinical Genomics Network.
