Lung tumors in 2 year old strain A/J mice exposed for 6 months to tobacco smoke

Summary adult strain A/J mice were exposed for 6 months in a whole-body inhalation chamber to a mixture of 89% sidestream and 11% mainstream cigarette smoke generated from Kentucky 1R4F research cigarettes. Chamber concentrations of smoke constituents were 158 mg/m3 of total suspended particulate matter (TSP). After an additional 4 months in air, some of the animals were killed. Lung tumor multiplicities in the smoke exposed animals were 1.8±0.2 versus 0.9±0.2 in controls. In animals kept beyond the age of 12 months, lung tumor multiplicities increased in both groups, but remained at all times twice the control values in the smoke exposed animals compared to controls (4.3±0.7 vs. 2.1±0.5 tumors per lung in 24 months old animals). Histopathology showed that, in 2 year old animals, still about 80% of tumors were of benign nature. No tumors were found in the nasal passages. It was concluded that tobacco smoke exposure not simply accelerates the development of lesions that eventually would have developed spontaneously, but induced de novo formation of lung tumors in A/J mice.