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Home News and Update Year 2011 Tooth-Decay Germs Tied to Bowel Cancer

Tooth-Decay Germs Tied to Bowel Cancer

Times of India
19 October 2011

A type of bacteria that cause dental decay and skin ulcers may also be linked to bowel cancer, say scientists who have found the bug in colon tumours.
According to two research teams, which have discovered the pathogen 'Fusobacterium' in bowel cancer tumours, say it's not yet clear if the bug might cause cancerous changes or whether it is just an incidental finding.
If the bacterium is to blame, antibiotics might be able to treat it and prevent cancer, they reported in the journal Genome Research.
Bowel cancer is the third most common cancer after after breast and lung.
Although the exact cause of bowel cancer is unknown, there are certain factors that increase risk, such as a strong family history of the disease and older age. Sarah Williams, of Cancer Research UK, said the research gave a clue about the environment in which bowel cancer grows. "It's early days and we look forward to the results of more specific, in-depth studies," Williams was quoted as saying by the BBC.

"In the meantime, people can reduce their risk of bowel cancer by not smoking, cutting down on alcohol, keeping a healthy weight, being active, reducing the amount of red and processed meat in their diet and eating plenty of fibre."

Together, the two research studies looked at more than 100 samples of healthy and cancerous bowel tissue and found the presence of the bug. They discovered the link by analyzing genetic material in tumor samples. They then subtracted human genes from the mix. What remained were microbe genes.

For years, Dr. Robert A. Holt, a genomics researcher at the British Columbia Cancer Agency, wrestled with a question about colon cancer. Might it be caused, or pushed along, by a bacterial infection?

Cancers of the liver, stomach and cervix have all been linked to microbes, he knew. And if there is one place in the body with a lot of microbes, it is the colon – microbial cells outnumber human cells there by a ratio of at least nine to one.

The new tools of genomic analysis offered an opportunity to look for a connection. What Dr. Holt and another group of researchers, working independently, have found is completely unexpected and puzzling. One particular species of bacterium never particularly prevalent in the colon seems to have a disturbing affinity for colon cancers.

The two research groups discovered the link by analyzing genetic material in tumor samples. They then subtracted human genes from the mix. What remained were microbe genes.

An analysis of these microbial genes showed that a type of bacterium, Fusobacterium, was abundant in the tumors although it normally is not among the more prominent species in the gut. Not only were the bacteria lurking around the cancer cells, but Dr. Holt found in subsequent experiments that they actually were burrowing into tumor cells – "which is kind of creepy," he said. An ability to invade cells, he said, is often what distinguishes a disease–causing microbe from one that is harmless.

Of course, that doesn't prove that Fusobacteria are causing tumors. They might just find the cancer cells a good place to live.
As Dr. Holt and his colleagues investigated further, they found the bacteria were especially prevalent in patients whose cancer had spread beyond their colons.
The finding could have been an anomaly. But, with no knowledge of Dr. Holt's results, Dr. Matthew Meyerson and his colleagues at the Dana–Farber Cancer Institute in Boston found the same thing. And while Dr. Holt's patients were from Canada, Dr. Meyerson's were from people in the United States, Vietnam and Barcelona, Spain. All had the bacteria in far greater abundance in their tumors than in normal colon cells.

"That, to me, was a real eye–opener," Dr. Meyerson said. He expected lots of different bacteria in the tumor tissue, he said. "It turned out not to be that way."

The two studies are published online Tuesday in Genome Research.
In their study, Dr. Holt and his colleagues began by looking at RNA, which reflects active genes, from 11 colon cancer patients. The colon cancer cells had an average of 79 times as many Fusobacteria as normal cells.

The investigators then looked for the bacteria in 88 more tumors and corresponding adjacent noncancerous colon cells, using probes for Fusobacteria genes. With that more sensitive method, they found an average of 415 times as many Fusobacteria in the tumor cells as in the normal cells.

Dr. Meyerson and his colleagues did similar experiments but looked at DNA, the gene sequences, instead of RNA. They began with nine patients, finding Fusobacteria DNA sequences mostly in the cancer tissue. Then they looked at cells from an additional 95 patients, searching specifically for Fusobacteria gene sequences. Again, the researchers found the bacteria in the cancer cells.

"I don't know what to make of it," Dr. Meyerson said. "The bacteria are hanging around the tumors, but I have no idea if they spur or cause cancer."

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