Colorectal cancer is one of the world’s most common cancers, with rising cases among younger adults. Now, researchers have found that this type of cancer is linked to a consistent gut microbiota signature, which may be partly modifiable through dietary fiber.

The findings, published in Cell Host & Microbe, suggest that this colorectal cancer-associated microbiota signature could help inform risk assessment, screening tools, and prevention strategies.

Many studies have linked colorectal cancer to changes in gut bacteria, including increases in microbes such as Fusobacterium, Peptostreptococcus, Parvimonas, and Porphyromonas. But so far, it was unclear whether this microbiota signal is reliable, including in early-onset colorectal cancer.

Selin Pekel at the European Molecular Biology Laboratory in Heidelberg, Germany, and her colleagues re-analyzed gut microbiota data from 6,779 stool samples and 906 tumor tissue samples across many colorectal cancer studies, using a method to reduce technical differences.

Robust signature

The researchers found a consistent cancer-associated bacterial signature across countries, sequencing methods, and early- and late-onset disease. Key bacteria, including Fusobacterium, Peptostreptococcus, Parvimonas, and Porphyromonas, were enriched in cancer tissue. 

Many cancer-linked bacteria seen in stool were present also in tumor tissue, even in early cancers. But stool tests picked up this signal less clearly, likely because tumor bacteria are diluted as they pass into stool.

The team then built a gut bacteria test using samples from 27 studies in 15 countries. It detected colorectal cancer fairly well, but not well enough to replace current screening tests, and it did poorly at spotting precancerous growths.

Dietary fiber

Cancer samples had more microbial genes linked to inflammation, cell attachment, and virulence, especially from Fusobacterium and Peptostreptococcus, the researchers found.

However, high fiber intake and fiber interventions were linked to lower cancer-associated microbiota signals. These findings support the idea, but do not prove, that the colorectal cancer-linked microbiota may be changeable, the authors say.

Regardless, they add, the work “strongly supports the existence of bacterial genera that are universally [colorectal cancer]-enriched across the globe, both in tumor tissue and fecal microbiome profiles.”