Spindle cell carcinoma of the hamster trachea induced by N-methyl-N-nitrosourea.

The tracheas of 63 male Syrian golden hamsters were exposed once each week for 12 weeks to a flowing stream of 0.5% N-methyl-N-nitrosourea in phosphate-buffered saline (pH 4.5) with a specially designed intratracheal cannula. The animals were killed when moribund or 6 months after the final exposure, and the respiratory tracts were examined grossly, histologically, and ultrastructurally for tumor formation. A total of 13 neoplasms was found in the larynx or trachea. Six were papillomas, 3 were carcinomas, and 4 were diagnosed as spindle-cell carcinomas. The average time of observation of the various tumor types was 33, 31, and 21 weeks, respectively. The spindle cell carcinomas contained an exophytic portion protruding into the tracheal or laryngeal lumen and an infiltrating portion growing circumferentially between the intact mucosa and the cartilage rings or plates. They were composed of sheets of elongated and spindle-shaped cells. Ultrastructurally, the cells contained bundles of tonofilaments and keratohyalin, and were connected by numerous desmosomes. These findings are consistent with a squamous origin of the tumor cells and a diagnosis of spindle cell carcinoma.