Dental Researchers Retract Statement Indicating Hydrogen Peroxide May Be Cancer Promoter

BUFFALO, N.Y. -- Authors of an abstract reporting preliminary results showing hydrogen peroxide may be a cancer promoter have retracted their presentation of study findings.

The study was conducted in the Department of Oral and Maxillofacial Surgery in the University at Buffalo School of Dental Medicine.

An abstract was published in conjunction with the joint meeting of the American Association of Dental Research and the International Association of Dental Research held March 10-13 in Vancouver, British Columbia, and a poster relating to the study was presented at the meeting.

"As authors on the abstract "Hydrogen Peroxide: A Promoter in Cancer Development," presented on March 12, 1999, at the combined meetings of the American and International Associations of Dental Research, we are retracting the presentation of study findings. Data obtained in that study were mistakenly interpreted as being suggestive of a link between the use of hydrogen peroxide or hydrogen peroxide-containing pharmaceuticals and oral precancerous lesions or frank cancerous lesions in humans.

"Briefly, this study utilized the hamster buccal-cheek-pouch model, and consisted of painting cheek pouches of the animals bilaterally with DMBA (0.5%9, 10-dimethyl-1, 2-benzantracene), a known carcinogen, for a period of six weeks, which ordinarily produces visible lesions that are characteristically premalignant. There were no macroscopically obvious visible lesions present at that time.

"Following the induction phase, the DMBA paintings were discontinued. After a period of one week, the right cheek pouches were treated three times weekly with 3 percent hydrogen peroxide only for a period of 12 weeks.

"Using a parenterally-administered fluorescence-producing substance and a photodetection device, fluorescence readings were obtained from the left cheek pouches and compared to those from the right cheek pouches in each animal. Any differences in fluorescence cannot be interpreted as being due to promotion of precancerous lesions or of cancerous lesions by hydrogen peroxide in this study.

"As stated in the original press release dated 3/12/99, this was only preliminary data, and as of now, no macroscopically visible cancers have been detected, nor have the study animals been subjected to analysis of tissue samples. This study does not demonstrate that hydrogen peroxide or dental products containing hydrogen peroxide as an active ingredient cause or promote oral cancers in animal models or in humans."

Once again, this abstract and any statements made by the authors at the IADR/AADR meeting or to the media regarding these research findings are being retracted."

The authors of the abstract are Barry C. Boyd, D.M.D., M.D., assistant professor; Thomas S. Mang, Ph.D, clinical associate professor, and Charles Liebow, D.M.D., professor, all of the UB Department of Oral and Maxillofacial Surgery, and student Thaun Loi.

VANCOUVER, British Columbia -- Scientists in the University at Buffalo School of Dental Medicine have preliminary evidence, based on research in an animal model, that hydrogen peroxide, a major ingredient in dental bleaches and in some whitening toothpastes, may be a cancer promoter.

"Our research appears to show that the use of hydrogen peroxide in certain strengths can promote lesions that have already begun to develop in the oral cavity," said Barry C. Boyd, D.M.D., lead researcher on the study. "The recent increase in oral use of hydrogen peroxide, especially with the advent of cosmetic dentistry, has brought this issue to the fore."

Results of the study were presented here today (March 12, 1999) at the combined meeting of the American Association for Dental Research and the International Association for Dental Research.

Earlier studies, including some done at UB, have shown mixed results on hydrogen peroxide's role as a possible cancer initiator and promoter, defined as an agent that can cause cancer only after cells already have begun to behave abnormally. The goal of the current study was to determine the rate of cancer progression, if any, when pre-cancerous cells were in frequent contact with hydrogen peroxide.

The researchers used photofluorescence as a measure of cancerous progression. Photofluorescence is based on the propensity of Photofrin, a light-sensitive drug, to accumulate in cancer cells. When exposed to light, cells that are changing or are already cancerous will stand out from normal cells due to the accumulation of the light-sensitive drug.

"There is a high correlation between increased fluorescence and neoplastic changes (abnormal cell growth)," Boyd said.

To examine hydrogen peroxide's cancer-promoting activity, researchers applied a 3-percent hydrogen-peroxide solution to premalignant lesions in the right cheek pouches of hamsters. Hydrogen peroxide was applied three times a week for 12 weeks.

Boyd said many dental practitioners use 3-percent hydrogen peroxide as a rinse or to debride oral wounds.

Lesions in the hamsters' left cheek pouches, not subject to hydrogen peroxide, served as controls.

Photodetection showed significantly more fluorescence in the cheek-pouch lesions exposed to hydrogen peroxide than in lesions not exposed. These findings suggest that this common bleaching agent may be a cancer promoter, Boyd said. He noted that a definitive answer is expected with the next phase of the research, which will be examination of tissue samples.

Additional researchers involved in the study were Thuan C. Loi, a dental student; Thomas S. Mang, Ph.D., clinical associate professor, and Charles Liebow, professor, all from the UB Department of Oral and Maxillofacial Surgery.