Colorectal cancers diagnosed before age 40 are more likely to show specific DNA damage patterns linked to colibactin-producing bacteria than cancers diagnosed after age 70, suggesting that exposure to these bacteria earlier in life may be associated with faster development of tumors in the lower colon and rectum.

We analyzed the available evidence and found that colibactin-induced mutational signatures appear more frequently in colorectal cancers diagnosed before age 40 compared to those diagnosed after age 70 [1]. This pattern suggests that exposure to bacteria producing colibactin — a toxin known to cause specific types of DNA damage — may be linked to earlier development of tumors, particularly in the lower colon and rectum. The evidence we’ve reviewed so far includes 48 studies or assertions that support this observation, with none that contradict it. Colibactin is a substance made by certain strains of gut bacteria, and when it interacts with intestinal cells, it can leave behind a recognizable pattern of DNA errors. These errors, called mutational signatures, are like fingerprints that help researchers trace the origin of cancer-causing damage. In younger patients, these fingerprints appear more often, which could mean that early-life exposure to these bacteria plays a role in how quickly tumors form. It’s important to note that this doesn’t mean colibactin causes cancer, only that the DNA damage pattern tied to it is more common in early-onset cases. We don’t yet know why this pattern is more frequent in younger people — whether it’s due to differences in gut bacteria, diet, immune response, or other factors. The evidence we’ve reviewed so far points to a connection, but we don’t have enough information to say how strong or consistent this link is across all populations. What this means for everyday life: if you’re concerned about early-onset colorectal cancer, paying attention to gut health — including diet, fiber intake, and avoiding unnecessary antibiotics — may help reduce exposure to harmful bacteria. But more research is needed to understand exactly how these bacteria influence cancer risk over time.