Bacteria in tumors may promote cancer

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Our bodies harbor countless microbes—and so do our tumors, it turns out. Over the past 5 years, researchers have shown cancer tissue contains entire communities of bacteria and fungi. 

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In a paper in Nature this week, a team led by Susan Bullman of the Fred Hutchinson Cancer Center reports that in oral and colorectal tumors, bacteria live inside cancer cells and boost their production of proteins known to suppress immune responses.  

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The study doesn’t entirely clinch the case for a bacterial role in cancer, but it is very suggestive, says Laurence Zitvogel, a tumor immunologist at the Gustave Roussy Institute. 

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“It shows that bacteria in colorectal and oral tumors can actively disturb the immune equilibrium,” she says. 

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Confirmation that microbes can cause tumors to grow or spread could open up new ways to make cancer treatment more effective, for instance by killing bacteria with antibiotics. 

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But the bacteria are taking them back a stage - like becoming a teenager again - where they can rapidly increase in number before maturing back into adulthood. 

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Straussman accidentally discovered that human pancreatic and colorectal cancer cells grown in the lab stopped responding to a cancer drug named gemcitabine when Mycoplasma bacteria were present in the culture. The bacteria, he discovered, “protected” the cells by producing an enzyme that breaks down gemcitabine. 

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When he studied 113 human pancreatic cancer samples, he found bacteria that produced the drug-chewing enzymes in 76% of them—raising the question of whether they contributed to drug resistance in human cancers.  

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