Protective Potential of Lactic-Acid Bacteria in Head and Neck Cancers

Objectives: Lactic acid producing streptococci and lactobacilli are part of the commensal flora and have been shown to exert protective effects against chronic inflammatory diseases and cancer. These beneficial bacteria increase mucosal protection, bind/degrade carcinogens, produce anti-tumorigenic compounds, and promote cell-mediated immune response. Dental caries is the demineralization of tooth structures by lactic acid formed by bacterial fermentation of dietary sugars. Studies suggest that cariogenic bacteria Streptococcus mutans and Lactobacillus casei, stimulate a highly polarized cell-mediated immunity. Methods: We performed a case-control study to test the association between dental caries and head and neck squamous cell carcinoma (HNSCC). Cases were patients newly diagnosed with primary HNSCC between 1999 and 2005 at Roswell Park Cancer Institute. Controls were new patients seen during the same time period as the cases but not diagnosed with cancer. Edentulous patients and those with a history of cancer or immunodeficiency were excluded. Dental caries and missing teeth were identified from panoramic radiographs taken at admission before the cancer treatment was initiated. Results: A total of 473 patients (266 cases and 207 controls) were included. Prevalence of dental caries and HNSCC were negatively associated (p<0.001, two-sided chi-square test). After adjusting for age at diagnosis, gender, race/ethnicity, missing teeth, alcohol and tobacco use in multiple logistic regression analysis, history of dental caries was associated with a 52% decreased risk of HNSCC (OR=0.48; 95% CI=0.28-0.81). Similar association between endodontic treatment (an objective measure of a long-standing caries history) and HNSCC (OR=0.57; 95% CI=0.33-0.98) strengthened the validity of the association between dental caries and HNSCC and suggested that this was not a chance finding. Conclusions: Commensal lactic acid bacteria may be an important player in the natural history of HNSCC. A direct causal association between specific bacteria and HNSCC needs to be confirmed in prospective clinical studies. T32-DE07034; R03CA119262.