PHILADELPHIA — Postmenopausal women with periodontal disease were more likely to develop breast cancer than women who did not have the chronic inflammatory gum disease, according to a study published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.
“Periodontal disease is a common condition, and it has been shown to be associated with heart disease, stroke, and diabetes,” said lead author Jo L. Freudenheim, PhD, distinguished professor in the Department of Epidemiology and Environmental Health in the University at Buffalo’s School of Public Health and Health Professions. “Previous research has found links between periodontal disease and oral, esophageal, head and neck, pancreatic, and lung cancers, so we wanted to see if there was any relationship with breast cancer.”
Freudenheim and colleagues monitored 73,737 postmenopausal women enrolled in the Women’s Health Initiative Observational Study, none of whom had previous breast cancer. Periodontal disease was reported in 26.1 percent of the women. Because prior studies have shown that the effects of periodontal disease vary depending on whether a person smokes, researchers examined the associations stratified by smoking status.
After a mean follow-up time of 6.7 years, 2,124 women were diagnosed with breast cancer. The researchers found that among all women, the risk of breast cancer was 14 percent higher in women who had periodontal disease.
Among women who had quit smoking within the past 20 years, those with periodontal disease had a 36 percent higher risk of breast cancer. Women who were smoking at the time of this study had a 32 percent higher risk if they had periodontal disease, but the association was not statistically significant. Those who had never smoked or had quit more than 20 years ago had a 6 percent and 8 percent increased risk, respectively, if they had periodontal disease.
Freudenheim said the fact that the highest risk was found in the smokers who had quit within the past 20 years may indicate that previous exposure to smoking affected the carcinogenic process, and that the effects of smoking were slow to be reversed. “We know that the bacteria in the mouths of current and former smokers who quit recently are different from those in the mouths of nonsmokers,” Freudenheim explained.
There are several possible explanations for the link between periodontal disease and breast cancer. One possibility is that there is a systemic inflammation with periodontal disease that affects the breast tissues. Another possible explanation is that bacteria from the mouth can enter the circulatory system and they affect breast tissues. However, further studies are needed to establish a causal link, Freudenheim said. “If we can study periodontal disease and breast cancer in other populations, and if we can do more detailed study of the characteristics of the periodontal disease, it would help us understand if there is a relationship,” Freudenheim said. “There is still much to understand about the role, if any, of oral bacteria and breast cancer.”
One limitation of the study is that women self-reported their periodontal disease status, after being asked whether a dentist had ever told them they had it. Also, Freudenheim pointed out that since her research focused on women who were already enrolled in a long-term national health study, they were more likely than the general population to be receiving regular medical and dental care, and were likely more health-conscious than the general population. She estimated that the general population would have a higher rate of periodontal disease and other risk factors, such as smoking, diabetes, and obesity.
This study was funded by the National Heart, Lung, and Blood Institute; the National Institutes of Health; and the U.S. Department of Health and Human Services. Freudenheim declares no conflicts of interest.