THE HISTOGENESIS OF RADIATION-INDUCED (Sr$sup 90$) SQUAMOUS EPITHELIAL CARCINOMA IN RAT LUNG. 1. CHANGES IN BRONCHIAL EPITHELIUM

Changes in bronchial epithelium were followed over a 6-month period in the lung of rats implanted with plexiglas capsules containing a mixture of Sr/sup 90/ and Y/sup 90/. In bronchi of all calibers, squamous epithelial carcinomas arose from a process which began as basal cell hyperplasia, leading to a replacement of the normal cylindrical epithelial cells. Metaplasia and neoplasia of bronchial epithelium under the influence of Sr/sup 90/ radiation is visualized as proceeding via the following steps: normal cylindrical epithelium -- basal cell hyperplasia yields transitional epithelium yields resting squamous epithelium yields proliferating squamous epithelium yields invasive carcinoma. Carcinomas developed most rapidly in proximity to the radiation source. (H.H.D.)