A surprising link between oral health and breast cancer has been revealed in a new study.
Researchers have discovered that a common bacterium associated with gum disease can enter the bloodstream and settle in breast tissue, where it causes DNA damage and speeds tumour growth and spread.
A study by John Hopkins Kimmel Cancer Center and Bloomberg-Kimmel Institute for Cancer immunotherapy also found that it appears to make cancer cells more aggressive and resistant to therapy.
"The key takeaway is that this oral microbe can reside in breast tissue and that there is a connection between this pathogen and breast cancer," said Dr Dipali Sharma, adding that the team's study was inspired by many small studies that looked at thousands of patients and connected periodontal disease to breast cancer.
"We wanted to dig deeper and see if we could uncover the underlying connections," said Dr Sheetal Parida, first author and a research associate working with Dr Sharma.
The study used mouse models and human breast cancer cells to reveal how the bacterium affected tissue.
Once it was introduced directly into breast ducts, it caused noncancerous changes accompanies by inflammation and DNA damage among other effects. Once introduced to the bloodstream, it significantly boosted the growth and spread of existing tumours.
A key biological process was also uncovered, which showed that exposure to the bacterium damaged cellular DNA and activated repair systems that are prone to errors.
One of these introduces mutations when rapidly reconnecting broken DNA strands, while short exposure also increases levels of a protein called PKcs, that is linked to cancer cell movement and chemotherapy resistance.
Cells that line the breast ducts and breast cancer cells carrying BRCA1 mutations were found to be more easily affected.
The study noted that further research is required to understand how this translates to patient care, and whether maintaining good oral health was relevant to breast cancer risks.
Dr Sharma said: "Our findings reveal a link between oral microbes and breast cancer risk and progression, particularly in genetically susceptible individuals.
“Nothing happens in isolation. The results suggest that multiple risk factors come together with F. nucleatum acting as an environmental factor that may cooperate with inherited BRCA1 mutations to promote breast cancer and tumour aggressiveness."
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