Cancers carry microbes with them when they spread around the body, suggesting that certain bacteria might speed up the progress of the disease.
New research by a team from Harvard University led by Matthew Myerson studied colon cancer specimens (in both primary and metastisised tumours) and found Fusobacteria microbes in almost all cases.
This was true even in cases where the samples were collected years apart.
"This strongly indicates that the cancers took the microbes with them when they spread and that the bacteria can persist for long periods of time within tumour cells," Dr Chris Smith of The Naked Scientists says.
"When the team transplanted human tumour samples into mice, either with, or without Fusobacteria, the tumours became established in the mice only in cases where the bacteria were present."
Meanwhile, treatment with the antibiotic metronidazole, which kills Fusobacteria, slowed the spread of tumours in the mice.