Induction of squamous cell carcinomas in the mouse lung after long-term inhalation of polycyclic aromatic hydrocarbon-rich exhausts.

A 10-month inhalation study using newborn female mice was performed to determine pulmonary tumorigenicity of polycyclic aromatic hydrocarbon (PAH)-enriched exhausts. At two exhaust doses containing 50 micrograms/m3 (group II) and 90 micrograms/m3 benzo(a)pyrene (BaP) (group III) a significant increase of lung tumors was observed and the incidence of malignant lung tumors was dose-dependent. Bronchiolo-alveolar adenomas were observed in all mice of groups II and III (40/40 each) as compared to 5/40 in the control (group I). Bronchiolo-alveolar adenocarcinomas developed in 10/40 and in 33/40 mice of groups II and III, respectively, but were absent in group I. Single or multiple squamous cell carcinomas, which showed variable degrees of differentiation were observed exclusively in 6 mice of group III. One adenosquamous carcinoma was seen in an further animal of this group.