Study links bacterial biofilms to increased colon and colorectal cancer risk.
Researchers from Johns Hopkins have found that dense mats of interacting bacteria, called biofilms, were present in the majority of cancers and polyps, particularly those on the right side of the colon. The presence of these bacterial bunches, they say, may represent an increased risk for colon cancer and could form the basis of new diagnostic tests. The study is published in the Proceedings of the National Academy of Sciences (PNAS).
Like tooth plaque and slime on pond stones, bacterial biofilms may coat the mucus layer of cells lining the colon, causing inflammation and some noncancerous bowel diseases. The researchers observed bacteria invading the layer of mucus that protects epithelial cells in these areas and upend the whole biology of the system.
In an examination of healthy and cancerous tissue biopsied from 118 people undergoing surgery or colonoscopy at The Johns Hopkins Hospital or at the University of Malaya Medical Centre in Malaysia, the found that biofilms were present on 89 percent of tumours, 13 out of every 15 cancers and four out of four polyps, removed from the right or ascending colon. By contrast, biofilms, for reasons not known, were found only 12 percent of the time on tumours on the left side of the colon, two of out of every 15 cancers and no polyps.
Overall, the researchers say, their data suggest the risk of developing colorectal cancer might be fivefold higher in patients with biofilms on the right side of the colon, compared to patients without the bacterial mats. The team add that what was so striking was that these biofilm-positive samples cluster so dramatically in the right colon. In fact, it’s virtually a universal feature of tumours that appear in that section of the colon, although the team don’t understand why.
The group hope the new findings can be used to develop a noninvasive test that detects these biofilms and uses them to predict a person’s risk of developing cancer. According to the team most colorectal cancers are known to develop slowly, over five to 10 years, and it’s a disease that’s curable if it’s diagnosed early.
Colonoscopies currently are the gold standard in detecting colorectal cancer, but only approximately 60 percent of people in the U.S. get them. At the same time, colonoscopies are less frequently performed outside the U.S., especially in low-resource countries, where colorectal cancers are on the rise, the team state. The researchers feel that they have an obligation to find better ways to diagnose this, because colonoscopies will not be done routinely in other parts of the world, and the medical community needs better tools to help prevent disease.
The research team also noted that probiotic treatments might be one strategy to reduce biofilms, but there is as yet no evidence that their use will reduce cancer risk or should be recommended to the public. The team theorise that biofilms induce inflammation, which in turn spurs genetic mutations in epithelial cells that make them prone to becoming cancerous. In the study, the scientists found a link between the presence of biofilms and biological changes associated with increased cell growth in the biopsied tissues.
The researchers also identified the types of bacteria found in the colon tissues through genetic sequencing. They found that the same species of bacteria were present in tumours from people with and without biofilms. This suggests that the biofilm itself, rather than a particular kind of bacteria, may be the cancer-causing trigger.
The lab’s earlier research looked at the role of bacteria and diarrheal disease, but over time they recognized that the bacteria triggered changes in cells that were consistent with the ability to induce tumours. And the researchers wondered whether colonization with these organisms might be a long-term trigger for colon cancer.
The researchers plan to examine biofilms in subjects over at least five years to see if they can understand the dynamics of their formation, persistence and relationship to early cancer development.