Induction of benign and malignant pulmonary tumours in mice with benzo(a)pyrene

Most of the pulmonary tumors induced by chemical carcinogens in mice are pulmonary adenomas. Because of the morphological and biological characteristics, the site of origin and the spontaneous occurrence of this type of tumour, the pulmonary adenoma system is generally not considered to be an adequate model for studies designed to elucidate the pathogenesis of human bronchogenic carcinoma. The present study was carried out to observe the histopathological changes in the lung of 4 strains of mice intratracheally instilled with benzo(a)pyrene(BP). On the other hand, for the carcinogenesis experiments using animals, a method studying the incidence of pulmonary adenoma in newborn mice has been generally adopted, but this method still needs more than 24 weeks. This experiment was one of the attempts to make such an experimental period shorter. For the latter experiment, both inbred A/J and noninbred N:GP(s) newborn mice were used. In the group given intratracheal instillation, squamous cell carcinomas and adenocarcinomas were induced. Tumous were induced in high incidence in the lung of A/J and C57Bl/6 mice. Squamous cell carcinomas especially were well differentiated in the A/J mice with a higher incidence than C57BL/6. In the group given subcutaneous injection, adequate combinations at week 9 for the application following anticarcinogenesis assay were the groups of A/J treated with 40 micrograms (71.0 % adenoma incidence) and N:GP(s) mice treated with 500 micrograms (49.4 % adenoma incidence) of BP. These findings suggest that mice appear adequate for studies on the pathogenesis of malignant lung tumours and detecting anticarcinogens.