Surprisingly, Kras point mutations were observed in only 6 lung tumors (3 sham, 1 3R4F, 1 THS 2.2 L, and 1 THS 2.2 H tumor sample), suggesting that point mutation is not the predominant cause for the proposed oncogene activation in 3R4F CS- or THS 2.2 aerosol-exposed mice. This evidence concerns the gene KRAS and neoplasm.