Histologic observations on the pathogenesis of lung cancer in hamsters following administration of polonium-210

A serial sacrifice experiment was carried out to study the site of origin and the stages in development of lung cancer in hamsters induced by polonium-210 (210Po). 1 or 2 animals were sacrificed weekly during and after a course of 7 intratracheal instillations of 0.1 μCi of 210Po in saline. This exposure produced a transient radiation pneumonitis of moderate severity during, and for several weeks after, the instillation period. Subsequent pathological changes included hyperplasia of bronchiolar epithelium, and focal proliferation of epithelial cells in peribronchiolar and more remote alveoli, termed epithelialization of alveoli. Hyperplastic bronchiolar epithelium frequently showed numerous Clara cells which exhibited pleomorphism of cells and nuclei, multinucleated cells, and striking changes in staining characteristics of secretory granules. Epithelialization of alveoli showed steady progression from well-circumscribed small foci to larger confluent lesions which were composed of various cell types and resembled tumors. Malignant tumors occurred in many animals surviving more than 24 weeks after the last instillation of 210Po