Are bacteria making colon cancers spread?

Cancers carry microbes with them when they spread around the body, suggesting that bacteria might promote the process, new research has revealed.

Rogue cancer cells don't operate alone, it seems: instead they can carry a cadre of microbial sidekicks that can accelerate the disease process.

This is the conclusion of a new study from scientists at Harvard, in Boston, who have looked at large numbers of tumour specimens collected from patients with colon cancer. The team, led by Matthew Myerson, also studied samples of metastases - tumours formed when cells break away from the primary site and become established in a remote part of the body - collected from the same patients.

In nearly all cases the team were able to culture microbes from a group known as Fusobacteria, as well as several other bacterial families, from the primary colon tumour samples. Surprisingly, in significant numbers of cases, genetically identical bacteria were also found clinging to the cells in the metastatic tumours, even in cases where the two 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.

These bacteria are not harmless hitch-hikers. 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.

Predictably, administering the antibiotic metronidazole, which kills Fusobacteria, to mice carrying human cancers significantly blunted tumour growth in the animals. Control mice given a different antibiotic, erythromycin, to which Fusobacteria are not sensitive, showed no such change in the growth trajectory of their cancers.

These results, say the team in a paper describing the findings in the journal Science this week, "point to the potential of Fusobacterium to contribute to colorectal cancer growth and metastasis."