Morphogenesis of neoplasms induced in the hamster trachea with N-methyl-N-nitrosourea

The tracheas of 95 male Syrian golden hamsters were locally exposed to a flowing stream of a 1% solution N-methyl-N-nitrosourea using a specially designed cannula at weekly intervals for 15 weeks. Animals were killed at specified times from 9 through 27 weeks following the first dose. Epithelial flattening was observed in over 90% of the tracheas throughout the study, but the proportion of the epithelium involved decreased from 100% at 9 and 16 weeks to 25 to 50% at 27 weeks. Hyperplastic foci of squamous metaplasia were found in 5% of the tracheas at 9 weeks, 90% of tracheas at 16 weeks, 83% of tracheas from 18 to 26 weeks, and 80% of tracheas at 27 weeks. Dysplastic foci of hyperplasia were observed in 5% of the tracheas at 9 weeks, 90% of the tracheas at 16 weeks, 17% of tracheas from 18 to 26 weeks, and 1% of tracheas at 27 weeks. Neoplasms were found in low incidences (2%) at 16 weeks. Papillomas and carcinomas were present in 13 and 42% of the tracheas from 18 to 26 weeks and 30 and 75% at 27 weeks, respectively. Dysplastic foci, as well as small focal carcinomas which had invaded the tracheal cartilages, were frequently found in close association with invaginations of the epithelium into the submucosa.