Dear Doctors: I recently read about a study that found a link between a certain kind of bacteria that lives in your mouth and the risk of developing colon cancer. I would like to know more details about that study, and also if this might point to a new approach in treatments.
Dear Reader: You are referring to the results of a study recently published in the journal Nature. It is part of an increasingly robust body of research that explores the potential role of bacteria, including oral microbes, in colorectal cancer. It's an important area of inquiry, as this form of the disease is the second-leading cause of cancer deaths in adults in the United States. Lung cancer remains the leading cause.
Last year, more than 153,000 new cases of colorectal cancer were diagnosed in the U.S., and the disease caused more than 52,000 deaths. Another disturbing trend is that colorectal cancers are beginning to be seen in a younger population, often in a more aggressive form. It is believed that by the start of the 2030s, the disease may become the leading cause of cancer deaths in people between the ages of 20 and 49.
In the study you are asking about, researchers focused on the microbiome of the mouth, which is home to more than 700 species of bacteria and over 100 different types of fungi. They were interested in learning which of those microorganisms might be able to survive the extreme environments of the digestive process and, thus, make their way to the large intestine. To do this, they examined tumors that had been removed from 200 colorectal cancer patients. The specific microbe they were interested in is Fusobacterium nucleatum. Also known as Fn, the bacterium lives in the oral cavity and is associated with gum disease.
In previous studies, the researchers had found that the presence of Fn in a colon tumor correlated with a decrease in survival rates. In this new research, they wanted to pinpoint if a specific form of the bacterium makes its way from the mouth to the colon. The answer to that question turns out to be yes. In analyzing the colon tumors, the researchers discovered unusually high levels of a subtype of Fn to be present in half of them. They also discovered that the subtype of Fn is actually a grouping of two different organisms, only one of which is associated with tumors.
You are correct that, in addition to shedding light on the potential causes of colon cancer, this research hints at a range of new treatments. Among the possibilities is the creation of lab-grown bacteria that would target and cause the death of specific cancer cells. Unlike the blunt-force tactics of chemo and radiation, which make no distinction between cancer cells and healthy tissues, this would constitute a precision attack on colorectal tumors. The research also opens up new possibilities in the arena of colon cancer screening. Among the possibilities are increasingly accurate fecal tests, and perhaps someday a blood test.
(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
