Can Your Body’s Bacteria Cause Cancer?

Inside the body’s microbiome

Doctors who treat patients with certain types of head and neck cancer frequently say they can smell a distinct odor on their patients. Loved ones often say the same.

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That’s an observation. But now, thanks to advances in genome sequencing, we might have an explanation backed by data. Could changes in the bacterial mix in these patients’ bodies cause the recognizable smell?

Welcome to the microbiome.

In microbiomics, we study the genome of the bacteria that lives on and in your body. We want to know how it interacts with your genes and affects the development of disease.

The gut bacteria H. pylori is the perfect example. In fact, when researchers discovered that H. pylori could lead not only to gastric ulcers, but also to gastric cancer, the field of microbiomics was born. Then it took technological advances such as genome sequencing and the ability to analyze “big data” for it to take off recently.

The bacteria-cancer connection

With head and neck squamous cell cancers — which account for more than 500,000 new cases each year — tobacco and alcohol use raise your risk.

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However, even with falling rates of smoking and drinking, the death rate for these cancers remains pretty consistent. So what else is going on? For an answer, we turn to the microbiome.

In a pilot study comparing 44 tumors to samples of normal tissue from the same patients, we found major differences in the microbiome. In the tumor samples, we saw increased methylation in four genes — MDR1, IL8, RARB, TGFBR2 — that are linked to these types of cancer.

Put more simply: Bacteria appear to interact with these genes. The bacteria seem to cause the genes to promote tumor growth rather than suppress it. On top of that, changes in the bacterial community in a tumor were associated with advanced cancers instead of early ones.

We are now working to validate these findings with more patients. We’ll also expand to other types of head and neck cancer where risk factors such as HPV and smoking are less of a factor.

Beyond the head and neck

Head and neck cancer is just a start. We also have begun projects to examine the microbiome in breast cancer, for example.

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That work will begin by looking at the microbiome in people’s mouths. Why the mouth, when cancer takes place in the breast? Because we think the microbiome in the mouth can metabolize things even in the rest of the body — including those that affect the origins and spread of breast cancer.

In some ways, microbiome research in cancer is behind the field in other diseases. For example, doctors battling the difficult gut infection C. difficile now have the option of fecal transplant.

But even in its early stages, cancer microbiomics is exciting.

One day, could we test for cancer before the cancer has even started using new, noninvasive biomarkers instead of blood tests and biopsies? And since we’re talking about bacteria, is there a future role for antibiotics or probiotics in treating or preventing cancer? Time and research will tell.

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Charis Eng, MD, PhD

Charis Eng, MD, PhD is founding chairwoman of the Genomic Medicine Institute and founding director of its Center for Personalized Genetic Healthcare. Dr. Eng is a global leader in cancer genetics and cancer genomic medicine.
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