A bacterium typically linked to periodontal disease, Fusobacterium nucleatum, could play an important role in the rising incidence of colorectal cancer in people younger than age 45. Another type of bacteria, Moraxella osloensis, has been found in colorectal cancer tumors at a nearly fourfold higher rate in patients older than 75 than in those younger than 45, demonstrating how differences in the bacteria that make up the body’s microbiome could affect cancer outcomes to varying degrees. These findings will be presented by Weinberg et al at the 2020 Gastrointestinal Cancers Symposium (Abstract 241).

Colorectal cancer incidence has been declining for several decades in people over age 55, in part because of the increased use of screening for the disease. Such screenings are generally not recommended for people under age 50. However, colorectal cancer rates have been increasing at nearly a 2% annual rate in people younger than 55 since 2006.

“We haven't seen large genetic differences in colorectal tumors from younger vs older people, so we hypothesize that something else, perhaps the microbiome, is contributing to the rise in incidence of the disease in younger people,” said first study author Benjamin Adam Weinberg, MD, Assistant Professor of Medicine at Georgetown Lombardi Comprehensive Cancer Center.

Methodology

Scientists have known that certain microbes that compose the microbiome—which consists of different types of bacteria, fungi, and viruses—can disturb the lining of the colon and promote tissue inflammation. This can result in mutations to the DNA of cells in the colon and lead to cancer. Researchers also know that F nucleatum can promote cancerous growth by suppressing immune responses in the colon.

To better understand the role of the microbiome in colorectal cancer, Dr. Weinberg and colleagues looked at the DNA and microbiome of archived tumors, as well as adjacent normal tissue when available, from 31 patients with colorectal cancer who were diagnosed before the age of 45 or after the age of 65.

Results

Overall, the investigators found 478 unique bacterial and fungal species in the tumors. One of the most common bacteria found was F nucleatum, which appeared in five of the younger patients’ tumors and in three of the older patients’ tumors. The researchers also found a significant difference in the rate of M osloensis (11% vs 46%) in younger compared to older patients. There was no significant difference in microbiome diversity in younger vs older patients.

“There was a much higher presence of F nucleatum in younger patients than we expected,” said Dr. Weinberg. “As to whether this bacterium alone can explain some of the rise in incidence of colorectal cancer in younger people is something we need to explore, and to aid in that effort, this ongoing study will incorporate tumors from up to a total of 144 people.”

Disclosure: This research was supported by the Colorectal Cancer Alliance and the Victoria Casey and Peter Teeley Foundation. For full disclosures of the study authors, visit coi.asco.org.