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Mysterious Bacterium Found Hiding In Human Tumors

Donna Marie Padua

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The stints of medical experts to understand the nature of different types of cancer, what causes them, how to treat them and how to prevent them continue. Just recently, researchers found a type of bacteria moving along with colon cancer cells and exists to survive in tumors. It is still unknown if the bacteria really cause colon tumors but the study gives hints that the organism may be “an integral part of cancer.”

The mysterious bacterium called Fusobacterium nucleatum was discovered to travel with colon cancer as it spreads throughout the body. However, whether it actually plays a role in causing or spurring the growth of cancer is still unknown.

Scientists found a bacterium moving long with colon cancer cells, they suspect have a link to its growth.

However, a new study published in the journal Science shows that antibiotics fight the bacteria and can slow down the growth of cancer. A series of experiments to prove the theory was done in four generations of mice.

As scientists grew suspicious that there may be a link between Fusobacterium nucleatum and colon cancer, the experts conducted experiments and found that most tumors host bacteria. However, only a small proportion of the cancer cells in any single tumor are infected by the bacterium. Colon cancer researcher at Johns Hopkins, Dr. Bert Vogelstein, said:

“The whole idea of bacteria in tumors is fascinating and unexpected.”

The Fusobacterium nucleatum was observed to live in the mouth of human colon cancer and travels to the liver and cancer spreads.

The study was initiated after Dr. Matthew Meyerson of the Dana-Farber Cancer Institute and Dr. Robert A. Holt of Simon Fraser University in British Columbia reported finding Fusobacteria inhabiting in the mouth of human colon cancers in 2011. Their discovery had researchers around the world studying colon cancer where a number of them also reported finding Fusobacteria in colon cancers.

The new paper, by Dr. Meyerson and his colleagues then came up with a paper to provide answers to the mystery. The team looked at human colon cancers that already spread to the liver. The liver tumors were then surgically removed and examined as long as two years after the operation.

From the study, the team found that colon tumors infected with Fusobacteria continued to be infected even after spreading to the liver. On the other hand, liver cancer cells containing the bacteria did not appear to be newly infected. Also, colon tumors that initially did not have the bacteria spread to the liver still not containing the organism. Dr, Meyerson explains:

“By far the most likely explanation is that the cancer metastasizes to the liver and carries this microbiome with it. The bacteria are not there by chance.
It’s kind of amazing that the bacteria are such an integral part of the cancer.”

Researchers transplanted the human cancer to mice to study how the bacterium really affect the cancer.

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A microbiologist and infectious disease specialist at Stanford and the Palo Alto VA, Dr. David Relman agreed:

“This really suggests they may be traveling with the cancer.”

To continue getting evidence and come up with a concrete conclusion, Dr. Meyerson and his team transplanted human colon cancers into mice. They observed the cancers grew. They plucked out pieces of the tumors and again transplanted them to other mice, where cancer again grew.

The procedure was repeatedly done up to the fourth generation of mice. Finally, the scientists saw the Fusobacteria remained with the cancers.

They tried to treat the mice with the antibiotic metronidazole which kills Fusobacteria. They found the infected tumors grew much more slowly. The other mice were treated with erythromycin which is an antibiotic that Fusobacteria resist. They then found the tumor growth unaffected.

The question now is whether to prescribe metronidazole to colon cancer patients whose tumors are infected with Fusobacteria. People are also wondering whether a vaccine against Fusobacteria will be developed to prevent colon cancer because of the results of the study.

Emma Allen-Vercoe of the University of Guelph who is also studying the bacterium’s true role in colon cancer advised taking things slow. She pointed out that the problem with antibiotics is that they kill not just Fusobacteria but lots of other bacteria as well. Those other species may be important in slowing the progression of colon cancer. She said:

“We don’t know enough yet to be able to predict the effects of a given antibiotic, and since everyone has a different gut microbiota, such a therapy will likely be hit and miss.”

Researchers are still finding out whether an antibiotic therapy can kill the bacterium as well as cancer.

One of the researchers, Dr. Holt, also pointed out another problem with the proposed treatment saying a patient should take the antibiotic indefinitely. This is due to Fusobacteria’s constant reintroduction into the mouth of cancer. Hence, if a person stopped the antibiotic treatment, the bacteria could once again get into their tumor cells.

In line with the suggested vaccine, Dr. Allen-Vercoe said not all strains of Fusobacteria are linked to cancer. She explained:

“Of the few strains that are, there is no clear consensus on why they are behaving pathogenically…And so there is no clear target for a vaccine strategy.”

To understand more about how Fusobacteria affects colon cancer growth, Dr. Vogelstein suggests the bacterium may not be directly causing cancer, but might be altering patients’ immune response. Dr. Relman also shared his suspicion saying perhaps the bacteria are acting more directly by secreting chemicals that spur growth in nearby cancer cells.

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