1987 Volume 26 Issue 3 Pages 412-426
Rabbits received intratracheal instillation of 1 mg of Nmethyl-N'-nitro-N-nitrosoguanidine (MNNG) once a week up to ten times. Thirty five rabbits were divided into 4 groups according to the duration of the experiment. Each of them was studied histopathologically and cytologically.
Various histopathologic changes w ere observed in the tracheobronchi of the rabbits. Early in the experiment, goblet cell hyperplasia and squamous metaplasia appeared. Then, mild to severe dysplasia were observed sequentially. Of 26 rabbits that received more than 6 mg of MNNG and survived for more than 8 week, 12 developed squamous cell carcinoma.
Cytologic specimens, such as tracheobronchial secretions, washings and imprint smears, were obtained at necropsy. In some rabbits, tracheal brushing through flexible bronchofiberscope was applied. In an early phase of the experiment, many bizarre cells were observed. These were thought to be cells of an early reaction type. Later in the experiment, atypical metaplastic cells appeared in all the cytologic material. We classified these cells according to the criteria being used in man, and the grading of the cellular atypia was well matched to the histologic diagnosis. Among 6 cancer-bearing rabbits, 2 had false negative cytological diagnoses, which was likely attributable to an incorrect sampling method. Brushing cytology was evaluated as a very useful method for repeatedly obtaining cytologic materials from the desired area.
During the development of experimental squamous cell carcinoma, we gave special attention to dysplasia, the frequency of which increased in proportion to the duration of the experiment and was higher in the rabbits with cancer than without. Moreover, dysplasia and basal cell hyperplasia were often found surrounding the foci of cancer.
We can use the flexible bronchofiberscope to detect induced cancer. This experimental model will be very useful to promote studies on human bronchogenic cancer of central type.
