Do Good Gut Bacteria Help Cut Lymphoma Risk?

Intestinal bacteria may be important in the development of a number of complex diseases.

Thinking of bacteria in terms of the infections and specific diseases they cause is deeply rooted in medicine. From the germs that cause flesh-eating infections or gangrene to the bacteria responsible for things like strep throat, sinus infections, and urinary tract infections, today microbes are still a powerful force to be reckoned with.

As scientific knowledge of bacteria and the human immune system advances, however, researchers have begun to confront the more subtle effects of bacteria – effects that may take place over years and involve multiple interactions and contingencies.

Such bacterial effects would not produce an infection as we have come to think of infections – that is, nothing noticeable such as pneumonia, or bloody diarrhea, or even as much as a fever or a sneeze.

Gut Bacteria: Friend or Foe?

Instead, they are seemingly innocent co-passengers in life – harmless squatters living in our intestines and other areas, otherwise known as the normal flora. Normal flora help us in many different ways, however, researchers believe that an imbalance in the types of bacterial hitchhikers found in the mix might have a role in complex diseases, such as autoimmune syndromes, allergies, and even cancer – that's the idea, at least.

Of course, the opposite may also true. The right balance of intestinal bacteria might actually have a protective effect over time in some cases. Cancer is a multifactorial disease, and no one is proposing gut bacteria alone hold the key to cancer prevention, but this is one of many avenues being explored.

Doctors have long known that particular species composition of the microscopic “garden” in the intestines can be important to health in illness. As scientists continue to learn new things about how the human immune system works, and how bacteria interact with it, the concept of the microbiome has emerged: the human microbiome refers to all of our microbes' genes and can be considered a counterpart to the human genome – all of our genes.

The genes in our microbiome outnumber the genes in our genome by about 100 to 1.

The concept of good and bad bacteria in the microbiome has made its way into the public consciousness as well, in the form of probiotics, prebiotics, and functional foods.

· Probiotic refers to live microorganisms that are intended to have health benefits.

· Prebiotics can be thought of as particular nutrients – often partially digestible carbohydrates – that “feed” the good bacteria, or otherwise potentially help to promote a good balance between beneficial and harmful gut bacteria.

· Functional foods are products that have a potentially positive effect on health, beyond basic nutrition.

As you can see, the way these terms are defined, there is no guarantee of effectiveness – which reflects the both the budding stage of the science and the complexity of proving that there are indeed benefits.

Bacteria and Cancer Risk

Scientists once believed that bacteria didn’t seem to have “the right stuff” to cause cancer, in contrast to viruses.

Even today, the list of viruses linked to cancer is very long compared with bacteria. And while it may be true that viruses can more easily fan the flames of malignancy development compared with bacteria, it is also true that bacteria are capable of contributing to the development of certain malignancies.

In the early 2000s, for instance, the bacterium Helicobacter pylori –​ known for its role in stomach ulcers – was clearly linked to gastric cancer.  Once considered “fringe scientists,” today many researchers looking into links between bacteria and complex diseases such as cancer are no longer considered unorthodox in their hypotheses and research efforts.

H. Pylori and Lymphoma

H. Pylori and MALT Lymphoma of the Stomach:

A rare type of non-Hodgkin’s lymphoma is associated with the bacterium H. Pylori. The cancer is called “marginal zone lymphoma of mucosa-associated lymphoid tissue,” or MALT, for short.

Gastric MALT lymphoma accounts for fewer than 1 in 20 cancers that start in the stomach. Gastric MALT lymphoma involves B-lymphocytes, a type of immune cell, in the stomach lining.

Coxiella Burnetii and Others

The bacteria that cause an infection called Q Fever –​ Coxiella burnetii –​ are excreted in milk, urine, and feces and present in the amniotic fluid of infected animals. Veterinarians and people who work with livestock are especially at risk. For some time, people with lymphoma were thought to be at increased risk for Q fever.

However, a study reported in the October 2015 issue of the journal “Blood” suggests people with Q Fever may actually be more likely to develop lymphoma. Investigators screened 1,468 patients treated at the French National Referral Center for Q Fever from 2004 to 2014 and found seven people who developed lymphoma after C. burnetii infection. Six patients were diagnosed with diffuse large B-cell lymphoma and one with follicular lymphoma. These and other bacteria may have a causal link to lymphoma in some cases, but research looking into this question is still ongoing.

Studying Lymphoma Risk and Gut Bacteria

Scientists at UCLA interested in how gut bacteria might affect the development of cancer have been testing their hypotheses in mice that have a diseased gene related to a human genetic disease, ataxia telangiectasia.

In humans, ataxia telangiectasia, or A-T, is a recessive genetic illness of childhood that occurs in one out of 100,000 people.  People with A-T tend to develop lymphoid malignancies at a greater rate than others. About 30 to 40 percent of A-T patients develop a cancer of some type during their life, and more than 40 percent of all tumors in A-T patients are non-Hodgkin’s lymphomas, about 20 percent are acute lymphocytic leukemias, and 5 percent are Hodgkin’s lymphomas.

In their animal studies, researchers used mice with a mutated ATM gene, responsible for high rates of leukemia, lymphomas, and other cancers.

Some mice were given only anti-inflammatory bacteria and others a mix of inflammatory and anti-inflammatory microbes. Results showed that lymphoma development was delayed in those mice receiving the anti-inflammatory bacteria alone.

How Might Gut Bacteria Decrease Risk?

Researchers then used a similar experimental design, involving the mice, to explore how gut bacteria might delay the onset of lymphoma. They found that those mice that received only the anti-inflammatory bacteria secreted metabolites known to prevent cancer in their feces and urine. Mice given these “good bacteria” also seemed to break down certain nutrients in a way that is believed to result in less cancer risk.

Mice given anti-inflammatory bacteria developed lymphoma more slowly than the comparator mice. The beneficial bacteria also increased the lifetime of the mice four-fold, and reduced DNA damage and inflammation.

The hope is that probiotics might one day help reduce the risk of developing cancer through these anti-inflammatory properties.


Cheema AK, Maier I, Dowdy T, et al. Chemopreventive Metabolites Are Correlated with a Change in Intestinal Microbiota Measured in A-T Mice and Decreased Carcinogenesis. PLoS One. 2016;11(4):e0151190.

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Melenotte C, Million M, Audoly G, et al. Bacterium that causes Q fever linked to non-Hodgkin lymphoma. Blood. 2015

Robbiani DR, Deroubaix S, Feldhahn N et al. Plasmodium Infection Promotes Genomic Instability and AID-Dependent B Cell Lymphoma. Cell 13 August 2015; 162 (4): 727–737.

Hansson LE, Nyrén O, Hsing AW, et al. The risk of stomach cancer in patients with gastric or duodenal ulcer disease. N Engl J Med. 2006; 335:242-249.

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National Cancer Institute. Helicobacter pylori and Cancer.

Melenotte C, Million M, Audoly G, et al. Bacterium that causes Q fever linked to non-Hodgkin lymphoma. Blood. 2015

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