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Experiments were conducted in order to examine the carcinogenetic process in young adult male beagles by attaching silicone rubber pellets containing 3-methylcholanthrene to the tracheal wall. Controls received silicone pellets without containing the carcinogen.The method was designed to induce msucoal stimulation. The pellets were surgically fixed on the mucosal epithelium of the cervical trachea and bronchoscopic examination was performed at 4-week intervals for a year.Polypoid lesions were recognized in 80% of the experimental animals and in all of the controls, within a period of 8-20 weeks after operation. Histologically, 3 types of lesions were recognized: squamous metaplasia, basal cell hyperplasia and inflammatory granuloma. In the control group, all polypoid lesions showed inflammatory granulomas. However, if pellets became detached the polypoid lesions decreased in size and finally disappeared.Pellets remained after 52 weeks in 15% of the experimental animal group. The amount of 3-MC released from the pellets totalled 1.0-1.1mg. In the group in which the pellets remained after 52 weeks, inflammatory granuloma with severe inflammation in the submucosal layer was recognized in all animals, but no malignant tumor was recognized histologically.The advantage of the present method is that it allows a sustained long-term release of the carcinogen that can be conjectured to reflect some types of human exposure to carcinogens. However, the influence of mechanical stimulation of the epithelium by the pellet, probably compounded by friction due to normal respiratory movement, must also be considered.

Experiments to induce tracheal cancer in beagle dogs by silicone pellets containing 3-methylcholanthrene.