Abstract
In order to examine the carcinogenetic process of squamous cell carcinoma of the lung, the authors observed chronologically the changes of the bronchial epithelium throughout the duration of the experiment which produced squamous cell carcinoma in dogs. The changes were observed cytologically, histologically and bronchofiber-scopically.
At the bifurcation of the apical and cardiac bronchi of two adult beagles and four adult mongrels a single dose of 50mg 20-methylcholanthrene (20-MC) was injected by means of a special needle which we developed for both therapeutic and experimental use through a bronchifiberscope at seven day intervals. Proliferation of basal cells accompanied by atypical nuclei or nuclear fission appeared immediately after injection of 20-MC, and were replaced by metaplastic cells after one week. Mildly atypical squamous cell metaplasia occured after 1-4 weeks, and moderately atypical squamous cell metaplasia after 2-8 weeks in all dogs. Five to nine weeks after the commencement of the experiment severely atypical squamous cell metaplasia appeared in 4 dogs, and in 3 dogs carcinoma in situ between 8 and 14 weeks. Invasive carcinoma developed after 18-22 weeks in 3 dogs (2 beagles, 1 mongrel). Squamous cell metaplasia was thus recognized to be an important precursor of squamous cell carcinoma, and further research on DNA analysis performed throughout the experiment may provide further elucidation of the carcinogenetic process.
