A new study indicates that specific types of bacteria that live in the gut are major contributors to lymphoma, a cancer of the white blood cells.

Up to 1,000 different species of bacteria live in the human gut. These bacteria, or intestinal microbiota, number 100 trillion cells. Over 90% of the cells in the body are bacteria. The composition of each person’s microbiome is very different. The differences are due to the types of bacteria people ingest early in their lives and also to the effects of diet and lifestyle.

In rodents, intestinal bacteria influence obesity, intestinal inflammation, and certain types of epithelial cancers. Epithelial cancers affect the coverings of the stomach, liver, or colon. However, little is known about the identity of the bacterial species that promote the growth of cancer or protect the body from cancer or how these species affect lymphoma.

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The research team, from the University of California-Los Angeles Jonsson Comprehensive Cancer Center, and led by Robert Schiestl, PhD, wanted to determine whether differences in peoples’ microbiomes affect their risk for lymphoma and whether changing the bacteria can reduce this risk. They studied mice with ataxia-telangiectasia (A-T), a genetic disease that is associated with a high rate of B-cell lymphoma in humans and mice. They discovered that, among mice with A-T, those with certain microbial species lived much longer than those with other bacteria before developing lymphoma. These mice also had less of the gene damage, or genotoxicity, that causes lymphoma.

“This study is the first to show a relationship between intestinal microbiota and the onset of lymphoma,” Schiestl said. “Given that intestinal microbiota is a potentially modifiable trait, these results hold considerable promise for intervention of B-cell lymphoma and other diseases.”

The scientists also were able to create a detailed catalog of bacteria types with promoting or protective effects on genotoxicity and lymphoma, which could be used in the future to create combined therapies that kill the bacteria that promote cancer (as antibiotics do) and increase the presence of the bacteria that protect from cancer (as probiotics do). The study was published in Cancer Research (2013;73(14):4222).