Gut microbiome may link genes, environment in colon cancer

Heidi Nelson, MD, FACS
Heidi Nelson, MD, FACS

It has long been known that environmental factors such as diet, smoking, and a sedentary lifestyle contribute to colon cancer. What has not been known is how. The gut microbiome may be the missing link.

“For our intestines, the closest, most intimate connection to the environment is through our gut microbiome,” said Heidi Nelson, MD, FACS, professor and chair of surgery, Mayo Clinic, Rochester, MN, and Medical Director, American College of Surgeons Cancer Programs. “The gut microbiome plays a role in both health and disease. It has its own metabolism and is part of our metabolism. That microbiome, that metabolism, could be the link between the environment and the development of colon cancer.”

Dr. Nelson will discuss the latest gut microbiome research and how it may one day affect colon cancer treatment during Wednesday’s annual Commission on Cancer Oncology Lecture, Microbes and Cancer: A Missing Link.

The gut microbiome is not just a collection of organisms; it’s an ecology, Dr. Nelson explained. If that ecology is in harmony, the host—your patient—is probably healthy. If the gut ecology is discordant, the host is less likely to enjoy good health.

The Western diet—high in meat, fat, and processed foods; low in grains, vegetables, and fiber—combined with little to no exercise, and too often marked by tobacco use and other insults—has long been associated with increased risk of colon cancer. But that knowledge has never been translated into a successful primary prevention strategy.

Colonoscopy and polypectomy have reduced rates of colon cancer, but that’s not primary prevention, Dr. Nelson noted. It’s simply an interruption of an ongoing process. Patients still develop polyps and those polyps can progress to colon cancer.

“Germline genetic contributions to colon cancer have been identified, and we have accordingly developed appropriate prevention strategies,” Dr. Nelson said. “If you have familial polyposis, you are at risk of cancer, and so we remove the colon to prevent cancer. If you have Lynch syndrome, you are at extremely high risk, and we modify screening protocols and apply prophylactic strategies. But when we get to the environmental factors, we have very little insight into how they cause cancer. That’s why microbiome research is so very exciting. There will someday be new therapies that affect our practice and our approach to colon cancer prevention.”

Nearly every part of the body that is exposed to the environment has its own microbiome, including the skin, mouth, lungs, and gut. Dysbiosis in any microbiome is associated with health conditions. Replacing an unhealthy gut microbiome with a healthier community can cure refractory clostridium difficile (CD) infection by restoring a balanced ecology in which CD cannot overgrow. Other manipulations of the gut microbiota could produce similar improvements in other conditions.

“After 50 years of knowing that something in our diet is creating the conditions for colon cancer, this is the first true optimism that we are going to figure out how red meat, for example, becomes colon cancer, if it actually does,” Dr. Nelson said. “It’s important to start thinking differently about the role of the gut microbiome and microbes in general; how they affect our health in both wellness and disease. Surgeons are going to be asked to play a major role in the scientific endeavors that help us understand why cancers develop and how to treat or even prevent cancers.”

The Commission on Cancer Oncology Lecture is sponsored by the Commission on Cancer. It was established in 1988 to explore major developments in oncology and to focus on the surgeon’s role in caring for cancer patients.