Histogenesis of Lung Tumors Induced in Rats by Inhalation of alpha Emitters. An Overview

摘要

Recent reviews have shown that simular risks coefficients for alpha irradiation of the lung in man could be deduced using epidemiological or experimental data in animals. Most experimental data were obtained in rats. In this overview the histogenesis and ultrastructure of lung tumors are presented. Only few tumors originating from lung parenchyma could be considered as non relevant for extrapolation to man. Most tumors arose from axial bronchus or bronchioles and their histogenesis was very similar to what is known in man. The only striking difference between the two species was related to the growth characteristics of the tumors. Tumors in rat, frequently papillary, acquired only slowly their full malignancy. They seem to be only potentially malignant. Two main types of tumors were considered: bronchogenic (B) and bronchiolo alveolar (b.a.) carcinomas. Survivals of the cancerous rats were log normal distribution in a given group of dose and were supposed to reflect latent period. No difference was found between B and b.a. carcinomas; geometric standard deviation did not increase when doses decrease. Since risk coefficients were found to increase when dose decreased, and through latent period fitted well with a power function of dose within the dose range studied, it is observed that the latent period can not be deduced by extrapolation at low doses. b.a. carcinomas prevailed at low doses; the relevance of this observation to man is however dubious since combined action with environmental carcinogens led to a high prevalence of B. carcinomas. Though genetic and immune surveillance are factors of some importance in the determination of the tumors it is suggested that critical individuals will be mostly multi-exposed individuals. (Atomindex citation 11:535411)