Fate of early carcinogen-induced lesions in tracheal epithelium.

Hyperplastic-metaplastic lesions were produced in transplanted rat tracheas by exposure to 310 or 75 mug 7,12-dimethylbenz(a)anthracene or to 650 mug benzo(a)pyrene delivered over a 2-week exposure period. Tissue recovery was studied for up to 16 weeks. After cessation of carcinogen exposure, most of the hyperplastic-metaplastic epithelium was rapidly replaced by mucociliary epithelium. In the 7,12-dimethylbenz(a)anthracene-exposed tracheas, a few mataplastic foci remained at 4 and 8 weeks. In all 3 exposure groups, portions of the mucosa were occupied by atrophic-pleomorphic epithelium that persisted throughout the observation period. The significance of these lesions in the evolution of neoplasia is as yet unknown. In vitro studies with epithelial cells derived from 7,12-dimethylbenz(a)anthracene-exposed tracheal transplants revealed that some cells have acquired a growth potential that is markedly different from that of normal mucociliary epithelium. This altered in vitro growth potential of epithelial cells may be an early indicator of an important event in the evolution of epithelial transformation in vivo.