Colon cancer: certain colon bacteria increase the risk

Colon cancer: certain colon bacteria increase the risk

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Study: These intestinal bacteria favor colon cancer

Colon cancer is one of the most common cancers in western countries. UK researchers have now found that people who have a certain type of bacteria in the gut may be at higher risk of developing colon cancer.

"We found evidence that the presence of an unclassified type of bacteria from a group of bacteria called Bacteroidales increased the risk of colorectal cancer by two to 15 percent," said Dr. Kaitlin Wade of the University of Bristol (UK) on Monday at the National Cancer Research Institute (NCRI) conference in Glasgow. "This means that people with this type of intestinal bacteria have a slightly higher average colorectal cancer risk than those who do not," the scientist said in a NCRI statement. "Our results support previous studies that showed that Bacteroidales bacteria are more likely and more abundant in people with colorectal cancer than in people without the disease."

Relationship between colon microbiome and colon cancer

The microbiome is a community of microorganisms, in this case bacteria that occur naturally in the body. There is growing evidence that the composition of the microbiome plays a role in human health and the body's susceptibility to disease. The human gut microbiome, which contains about three trillion bacteria, supports digestion and protects against infections. It is determined by the individual genetic makeup of a person and their equipment and is therefore unique for each person. It also remains relatively stable throughout life unless it is affected by antibiotics, illness, or a change in diet, among other things.

Dr. Wade said, "It was interesting to see whether changes in the human gut microbiome, such as the number of bacteria or simply the number of different types of bacteria, could affect colon cancer. Many studies in mice and humans have shown a link between colon microbiome and colon cancer, but few have provided convincing evidence of causality. In other words, it is really difficult to determine whether components of the gut microbiome can cause colon cancer, whether the disease itself changes the gut microbiome or whether the association is due to other factors. ”

Data from various studies used

The Mendelian randomization, with which the researchers have worked, uses complex statistical analyzes of data from large populations to provide clues to cause and effect and not just the existence of an association. This method for non-experimental studies to determine the impact of changing risk factors should help "determine whether people with a different genetic makeup and therefore different gut microbiome profiles have a different risk of colon cancer," said Dr. Calf.

Thanks to this method, the researchers did not have to work directly on the intestinal microbiome, for example by administering antibiotics or probiotics in a randomized study, and there was also no need to wait and see whether people developed colon cancer. "We only need studies in which this information has already been measured."

According to the information, the researchers used data from 3,890 people who had participated in the "Flemish Gut Flora Project", in the "German Food Chain Plus study" and the "PopGen study", and in 120,328 people from the "Genetics and Epidemiology of" Colorectal Cancer Consortium ”(GECCO). These studies looked for small variations in the genome of participants that occur more frequently in people with a certain disease or specificity than in people without this disease or specificity - so-called genome-wide association studies (GWAS).

They found that the genetic variation in the population in certain parts of the genome was related to the presence or the different amount of 13 types of intestinal bacteria and that people with an unclassified type of bacteria from the Bacteroidales group had a higher risk of colon cancer than humans without these bacteria. Dr. Wade said that their results must be replicated by other studies using different data and methods before the effects on human health can be fully understood.

More research needed

“We need to classify the exact species or strain of the bacteria in the Bacteroidales group and do more work to understand how and why human genetic variations can alter the gut microbiome. While these results show that these bacteria can cause colorectal cancer, we don't know whether trying to change them to reduce the risk of colorectal cancer could have other unforeseen effects on other aspects of health, ”the researcher says.

"However, I believe that we are at the forefront of understanding and assessing the complexity of these relationships - not only between the human gut microbiome and the disease, but also between human genetic variation and the gut microbiome itself - and this is appropriate These methods have to be used to assess causality, ”concluded Dr. Calf.

Analysis of genetic associations

“Mendelian randomization methods are increasingly used routinely to provide clues to causal risk factors by analyzing genetic associations with a disease and with risk factors. This is one of the first studies to use these methods to provide insight into the reasons for the postulated and plausible but largely unproven connections between microbiome and colon cancer, ”said Professor Ian Tomlinson of the University of Edinburgh and member of the scientific committee of the NCRI conference .

“The stability of the gut microbiome is questionable and there are complex relationships between the species and the number of bacteria present. It is therefore too early to attribute causality to the reported results. However, similar larger studies have the potential to significantly improve our understanding of colorectal cancer, ”said the scientist, who was not involved in the study. (ad)

Author and source information

This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.


  • University of Bristol: Researchers identify certain gut bacteria that may be involved in causing bowel cancer, (accessed: November 4, 2019), University of Bristol
  • National Cancer Research Institute: Researchers identify certain gut bacteria that may be involved in causing bowel cancer, (accessed: November 4, 2019), National Cancer Research Institute

Video: Dr. Sears on Microbiota in Colon Cancer (November 2022).