Cancer treatment could be adapted to account for the large concentrations of bacteria in the colorectal form of the disease.
Scientists working at the Dana-Farber Institute and the Broad Institute sequenced the DNA of tumours and then compared the results to DNA of tissues in healthy people.
Large amounts of Fusobacterium DNA were found in the tumour sequences.
"There has been an increasing focus on the relationship between cancer cells and their 'microenvironment', swap specifically on the cell-to-cell interactions that may promote cancer formation and growth," said the study's senior author Matthew Meyerson.
He stressed that the bug may not be the cause of colorectal cancer but the relationship does warrant further study as future treatments could use these findings about the tumour's microenvironment to be more effective.
Current treatment strategies have seen the survival rates of the disease improve with 50 per cent of patients surviving ten years after diagnosis, according to Cancer Research UK.