Have you ever wondered why some colon cancers start in the rectum while others appear higher up? A new study looked at tiny samples of colon tissue from people who had colonoscopies. Researchers examined 125 individual tissue samples from six different areas of the colon. They used advanced DNA sequencing to look for specific mutations caused by a toxin called colibactin, which is produced by certain strains of E. coli bacteria.
The results showed a clear pattern in the rectum. Both people with polyps and those without had significantly more of this specific DNA damage in their rectum compared to other areas. This damage matches a unique signature left behind by colibactin. However, when researchers looked at the total amount of this damage across different groups, they found no significant difference between people with no polyps, those with polyps, and those with colorectal cancer.
This study argues against the idea that colibactin directly causes colorectal cancer in a general sense. Instead, the findings suggest the toxin creates a specific type of genetic change only in the lower part of the colon. This anatomic specificity might explain why early-onset colorectal cancer is often found in the distal colon. While this helps us understand regional risks, the reasons for the recent rise in early-onset cancer remain unclear, and more research is needed to see if this damage leads to disease.