Scientists have discovered that a common type of oral bacteria can make some cancers "melt away".
Researchers at Guy's and St Thomas' and King's College London said they were "surprised" to discover that fusobacterium - a type of bacteria commonly found in the mouth - appears to have the ability to kill some types of cancer.
According to a study, people with head and neck cancer who were found to have this bacteria inside their cancer were found to have much better outcomes.
Researchers are now looking at the exact biological mechanisms behind the link and the initial findings, he said The Guardian.
Dr Miguel Reis Ferreira, first author of the study and a head and neck cancer consultant at Guy's and St Thomas', told the PA news agency:
"Basically, we found that when you find these bacteria inside head and neck cancers, they have much better outcomes. The other thing we found is that in cell cultures this bacterium is capable of killing cancer.
What we're finding is that this little bug is causing a better outcome based on something it's doing inside the cancer. So we're looking for that mechanism at the moment and it should be the subject of a new paper in the very short future."
He added: "This research reveals that these bacteria play a more complex role than previously known in their relationship with cancer, that they essentially melt away head and neck cancer cells. However, this finding must be balanced by their known role in worsening cancers such as those in the bowel."
The scientists used the modeling to help identify bacteria that might be of interest to investigate further.
They then studied the effect of the bacteria on cancer cells in a laboratory and also performed an analysis of data on 155 head and neck cancer patients whose tumor information had been submitted to the Cancer Genome Atlas database.
Academics initially expected a different result as previous research has linked fusobacterium to bowel cancer progression.
In laboratory studies, researchers placed amounts of bacteria in Petri dishes and left them for several days. When they returned to inspect the effect of the bacteria on the cancer, they found that the cancer had almost disappeared.
They found that there was a 70%-99% reduction in the number of viable cancer cells in head and neck cancer cells after they were infected with fusobacterium.
Analysis of patient data found that those with fusobacterium within their cancer had a better chance of survival compared to those who did not.
The detection of fusobacterium in head and neck cancers was associated with a 65% reduction in the risk of death compared with patients whose cancer did not contain the bacteria.
Researchers hope the discovery could help guide treatment for patients with head and neck cancers, which include cancers of the mouth, throat, voice box, nose and sinuses.
Experts said there had been few therapeutic advances in head and neck cancer in the past 20 years, so it was hoped the discovery could lead to new treatments in the future.
Reis Ferreira said that before the lab work, the team had expected that fusobacterium would encourage these cancers to grow or make them more resistant to radiotherapy. But they actually found that “at the end of a few days it just completely destroys the cancer."
"You put it in cancer in very low amounts and it just starts killing it very quickly," he said.
Dr Anjali Chander, a senior clinical researcher at King's College London and lead author, said: "Our findings are remarkable and very surprising. We had a eureka moment when we discovered that our international colleagues also found data that corroborated the discovery.”
Barbara Kasumu, chief executive of Guy's Cancer Charity, which helped fund the study, said:
"We are proud to support the groundbreaking research conducted by Miguel and Anjali, which aims to improve our understanding of head and neck cancer and develop more compassionate and effective treatments."
