Experimental Tumor Induction in a Circumscribed Region of the Hamster Trachea: Correlation of Histology and Exfoliative Cytology2

A method for the induction of carcinomas in a circumscribed region of the hamster trachea is reported. By means of a special catheter, a solution of N-nitroso-N-methylurea was applied twice a week to about a 6-mm length of the trachea 10- to 16-mm distal from teh vocal cords. Slight alteration of this catheter allowed sampling of cytologic specimens directly from the surface of the carcinogen0exposed epithelium. This procedure permitted the simple and accurate correlation of sequential histologic and cytologic changes observed during tumor development in the hamsters. Noninvasive dysplastic and metaplastic lesions were seen in animals killed after 5 and 10 weeks of carcinogen application. These epithelial changes could be readily correlated with abnormal exfoliated cells abundantly present in cytologic specimens from these animals. Exposure to carcinogen for 15 weeks induced a 100% tumor incidence exclusively at the application site. More than 75% of the malignancies appeared within 15-20 weeks after the start of carcinogen administration. Most tumors were epidermoid carcinomas but some anaplastic large-cell carcinomas were also observed. Cytologic specimens of tumor-bearing animals had many cells conclusive of malignancy. The new experimental system lends itself to study of the effect of topically applied anticarcinogenic or cocarcinogenic agents on different carcinogen-induced epithelial lesions whose regression or progression can be followed by exfoliative cytology.