Invasive
carcinoma of the larynx was induced in 36.8% of inbred Syrian golden hamsters from strain B10 15.16, susceptible to this type of
cancer when exposed to
smoke from reference filter cigarettes for 59-80 weeks. Nearly half the animals (47.4%) showed
laryngeal cancer, including noninvasive
carcinoma and
carcinoma in situ, which occurred with daily
smoke exposures (twice a day for 12 min each time, for 27 sec out of each min) 7 days a week at
smoke concentrations of 22%. When the
smoke concentration was reduced to 11%, the number of induced lesions was reduced proprotionately. When a portion of tobacco was replaced in the cigarettes by a tobacco supplement,
Cytrel (a trademark of the Celanese Corp., Charlotte, N.C.), a reduction of
carcinogenesis proportionate to the
Cytrel content of the cigarette took place.
Smoke from cigarettes containing only
Cytrel and no tobacco induced no
carcinomas under the conditions used. Other dose-related changes observed were laryngeal
papillomas, laryngeal epithelial
hyperplasia, tracheal epithelial
hyperplasia, and
metaplasia and accumulation of alveolar macrophages. Tar deposition in lungs and accumulation of alveolar macrophages. Tar deposition in lungs and larynges was determined in a separate study by means of a marker,
decachlorobiphenyl, added to the cigarettes. Admixture of
Cytrel to cigarettes reduced tar deposition in the respiratory tract, which paralleled the decrease in the incidence of laryngeal
carcinoma. However, the amounts of tar deposited in the larynx when 100%
Cytrel was smoked were still significant, even though no
carcinomas were observed. Thus
smoke from
Cytrel tobacco supplement may be less carcinogenic than equal amounts of tobacco
smoke.