With colon cancer on the rise among younger Americans, researchers are working to figure out why.
A new study suggests the microbiome — the community of microorganisms in the body — may play a role.
“Younger people with colorectal cancer have more biologically aggressive cancers and whatever survival benefit they have by being younger is outweighed by the more aggressive tumor biology. We also know, that for the most part, genetics doesn’t explain the recent rise in young-onset disease,” said Dr. Benjamin Weinberg. He is an associate professor of medicine at Georgetown University's Lombardi Comprehensive Cancer Center, in Washington, D.C.
“But we have trillions of bacteria residing in our body, including in our gut, some of which are implicated in the development of colorectal cancer, hence we think the microbiome may be an important factor in the development of the disease as it is involved in the interplay between a person’s genetics, environment, diet and immune system,” Weinberg added in a news release from the American Society of Clinical Oncology (ASCO).
The findings are scheduled for presentation in June at the society's annual meeting, in Chicago. Research presented at medical meetings should be considered preliminary until published in a peer-reviewed journal.
The number of young adults diagnosed with colon cancer in the United States nearly doubled over 25 years. The incident rate was 11% in 1995 and 20% in 2020, according to the American Cancer Society.
Studying the microbiome of colon cancer patients, the researchers saw that bacteria, fungi and viruses in patients’ tumors varied widely depending on whether they had early-onset disease (age 45 or younger) or late-onset (age 65 or older).
Certain microbes can disturb the lining of the colon. This promotes tissue inflammation and can result in mutations to the DNA of cells in the colon, leading to cancer, the study authors noted.
One particular type of bacteria, Fusobacterium nucleatum (F. nuc), can suppress immune responses in the colon, allowing cancer to grow.
For this study, the researchers looked at the DNA and microbiome of tumors from 36 patients diagnosed with colon cancer before age 45. They also looked at specimens from 27 people diagnosed after age 65.
The investigators detected 917 unique bacterial and fungal species in the tumors.
Among the most common was F. nuc, which appeared equally in about 30% of both early- and late-onset tumors.
Cladosporium sp. was found more commonly in early-onset cancer. Pseudomonas luteola, Ralstonia sp., and Moraxella osloensis were seen more in older patients.
Others were found only in the microbiome of people with late-onset disease.
The researchers plan to continue exploring the relationship between the microbiome and other factors that contribute to colon cancer.
“Because we have tumor genetic data and diet questionnaire results from many of our patients, we hope to explore more relationships and other aspects of how the microbiome impacts colorectal cancer progression in the future,” Weinberg said. “We are also interested in the circulating microbiome, such as bacteria that could be picked up in a blood sample, and how this correlates with bacteria in the gut and in the tumor.”
The American Cancer Society has more on colon cancer.
SOURCE: American Society of Clinical Oncology, news release, May 25, 2023