Researchers say they have uncovered how bacteria may set off a chain reaction leading to bowel cancer.
Fusobacteria, commonly found in the mouth, cause overactive immune responses and turn on cancer growth genes, two US studies reveal.
The microbes had been linked with colorectal cancer before but it was not known whether they were directly involved in tumour growth.
The early findings are published in the journal Cell Host & Microbe.
In addition to potential new treatments, the discovery could lead to better early diagnosis and prevention, experts hope.