Although smokeless tobacco products have long been linked with certain cancers, including those of the oral cavity and esophagus, this is the first study to identify a specific chemical present in smokeless tobacco products that induces oral cancer in animals, according to Silvia Balbo, PhD, research associate at the Masonic Cancer Center of the University of Minnesota.
"(S)-N'-nitrosonornicotine, or (S)-NNN, is the only chemical in smokeless tobacco known to cause oral cancer," Balbo said in a press release.
Balbo and colleagues administered (S)-NNN and (R)-NNN to four groups of 24 rats. The rats were given either (S)-NNN alone, (R)-NNN alone, a combination of both, or tap water. The total dose was approximately equivalent to the amount of (S)-NNN to which a smokeless tobacco user would be exposed from chronic use of these products.
All rats assigned to (S)-NNN alone or the combination of the two began losing weight after one year of exposure and died by 17 months. Rats assigned to (R)-NNN or tap water were terminated at 20 months.
All rats assigned to (S)-NNN had esophageal tumors and demonstrated 100% incidence of oral tumors, including tumors of the tongue, buccal mucosa, soft palate, and pharynx. In contrast, researchers found oral tumors in only five of 24 rats given (R)-NNN and esophageal tumors in only three of 24 rats assigned to (R)-NNN.
Twelve rats given the combination of (S)-NNN and (R)-NNN had 153 esophageal tumors and 96 oral tumors.
Since the U.S. Food and Drug Administration regulates tobacco products, Balbo hopes the results of this study will inform regulatory decisions. Moving forward, she and her colleagues hope to identify other chemicals that may be carcinogens in smokeless tobacco and to understand what level of these chemicals is present in smokeless tobacco products.
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