Study links oral bacterium to breast cancer development

Iveta Ramonaite, Dental Tribune International

Tue. 28. April 2026

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BALTIMORE, US: Growing evidence suggests that the oral microbiome may influence the development of cancers beyond the oral cavity. In a recent preclinical study, researchers investigated whether a specific oral bacterium associated with periodontal disease could be considered a breast cancer risk factor. Their findings indicate that the bacterium may contribute to breast cancer development and progression. The results add to an emerging body of evidence on the systemic impact of oral pathogens and underscore the importance of oral health in overall disease prevention.

Prof. Dipali Sharma of Johns Hopkins University was part of a recent study that has made novel and meaningful findings on a potential link between oral bacteria and breast cancer development. (Image: Prof. Dipali Sharma)

Senior author Dr Dipali Sharma, professor of oncology at the Johns Hopkins University Sidney Kimmel Comprehensive Cancer Center in Baltimore, told Dental Tribune International that the research was motivated by emerging evidence linking oral disease with cancer. She noted that certain oral pathogens, such as those closely associated with periodontal disease, may have broader biological effects beyond the oral cavity.

“We found that F. nucleatum was present in breast cancer tissue. Interestingly, the abundance of these bacteria in breast tumours positively correlated with the oral levels of these opportunistic pathogens in the same patient,” Prof. Sharma explained.

“We also observed that healthy mice that were given F. nucleatum developed mammary gland hyperplasia in a few weeks. Also, tumour-bearing mice exhibited accelerated breast tumour growth upon exposure to F. nucleatum. These pathogenic bacteria also imparted breast cancer cells with higher migration and invasion capabilities, which are key features associated with metastatic progression,” she commented.

The team also identified a possible mechanism behind these effects. In laboratory models, breast cells exposed to F. nucleatum showed DNA damage and changes in the way breast cells repaired that damage. Exposed breast cells also showed features associated with more aggressive tumour behaviour, including greater migration, invasion and self-renewal, as well as a reduced sensitivity to therapy. The effect appeared to be especially pronounced in breast cells with mutations in BRCA1, a gene involved in DNA repair and breast cancer susceptibility. These cells showed greater uptake and retention of the bacterium, a finding that the researchers linked to higher levels of a surface sugar that helps the microbe attach to and enter cells.

Prof. Sharma said the findings raise broader questions about the possible relationship between periodontal disease and breast cancer risk, particularly in women with mutations in BRCA1. She explained that cancer is a multifactorial disease influenced by both modifiable and non-modifiable risk factors. While genetic predisposition plays a role, factors such as oral health and the balance of the oral microbiome may form part of wider prevention strategies. In this context, she noted that good oral hygiene and timely treatment of periodontal disease may be important.

However, she cautioned that the study did not establish a causal link between periodontal disease and breast cancer. Further studies are needed to determine the clinical relevance of these findings, including whether oral health status could play a role in assessment of breast cancer risk.

The study, titled “A pro-carcinogenic oral microbe internalized by breast cancer cells promotes mammary tumorigenesis”, was published online on 15 January 2026 in Cell Communication and Signaling, ahead of inclusion in an issue.