Two new studies from researchers at Fred Hutchinson Cancer Center in Seattle reveal how bacteria infiltrate tumors and could be helping tumors progress and spread. The research team also showed that the different microbial players in a tumor’s microbiome could influence how a cancer responds to treatment.

The findings also suggest a link between oral health and cancer, as microbes in the mouth are associated with cancers elsewhere in the body.

The two papers — one published Nov. 15 in Cell Reports and the other published Nov. 16 in Nature — focus on an oral bacterium called Fusobacterium nucleatum, which has been linked to colorectal cancer.

Tumors often have help in their efforts to survive and grow. Non-cancerous cells around a tumor can help it avoid attacks by the immune system, resist therapies that target them and allow it to spread to other parts of the body. Researchers are now finding that some of these helpful neighbors aren’t even human cells — they’re bacteria.

“What we’re showing is that there are regions of the tumor that are heavily colonized by bacteria — micro-niche regions — and they differ functionally from regions that do not harbor bacteria,” said Fred Hutch cancer microbiome researcher and study co-lead Susan Bullman, PhD, referring to the work outlined in the Nature study. “And these bacteria-rich regions have increased metastatic potential.”

Bullman and her collaborator, Fred Hutch molecular microbiologist Christopher D. Johnston, PhD, combined observations from tumors with lab-based experiments and small-molecule drug screens to show that F. nucleatum may shape conditions in tumors to keep them safe from immune attack and help them spread through the body. They discovered that some cancer therapeutics may work because they not only target tumor cells, but also the bacteria that are helping them.

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