Scientists have discovered that a common type of mouth bacteria can make certain cancers “melt”. Researchers at Guy’s and St Thomas’ and King’s College London said they had been “brutally surprised” to find that fusobacterium – a type of bacteria commonly found in the mouth – appears to have the ability to kill certain cancers. People with head and neck cancers who were found to have this bacteria within their cancer have been found to have much better outcomes, according to a study. Researchers are now looking into the exact biological mechanisms behind the link after the initial findings. Dr Miguel Reis Ferreira, the study’s senior author and a consultant in head and neck cancers at Guy’s and St Thomas’, told the PA news agency: “In essence, we found that when you find these bacteria within head and neck cancers, they have much better outcomes. The other thing that 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 that it’s doing inside the cancer. So we are looking for that mechanism at present, and it should be the theme for a new paper in the very short-term 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 head and neck cancer cells. However, this finding should be balanced by their known role in making cancers such as those in the bowel get worse.” Scientists used modelling to help identify which bacteria may be of interest to further investigate. Then they studied the effect of the bacteria on cancerous cells in a laboratory and also performed an analysis of data on 155 patients with head and neck cancer whose tumour information had been submitted to the Cancer Genome Atlas database. Academics initially expected a different outcome as previous research has linked fusobacterium to the progression of bowel cancer. In the lab studies, researchers put quantities of the bacteria in petri dishes and left them for a couple of days. When they returned to inspect the effect of the bacteria on the cancer, they found that the cancer had almost disappeared. They found there was a 70%-99% reduction in the number of viable cancer cells in head and neck cancer cells after being infected with fusobacterium. Analysis of the patient data found that those with fusobacterium within their cancer had better survival odds compared with those who did not. Fusobacterium detectability in head and neck cancers was associated with a 65% reduction in risk of death compared with patients whose cancers did not contain the bacteria. Researchers hope the finding could help guide treatment for patients with head and neck cancer, 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 last 20 years, so it was hoped the finding could lead to new treatments in the future. Reis Ferreira said that before the lab work, the team had expected fusobacterium to 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 destroys the cancer completely”. “You put it in the cancer at very low quantities and it just starts killing it very quickly,” he said. Dr Anjali Chander, a senior clinical research fellow at King’s College London and the lead author, said: “Our findings are remarkable and very surprising. We had a eureka moment when we found that our international colleagues also found data that validated the discovery.” Barbara Kasumu, the executive director 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 enhance our understanding of head and neck cancer and develop more compassionate and effective treatments.”